Process and apparatus for recovering oligomerate

ABSTRACT

A process and apparatus uses a flash drum to separate light hydrocarbons from heavy oligomerate from an oligomerization zone. The heavy oligomerate can bypass a fractionation column in the oligomerate recovery section and be recycled to the oligomerization zone or other zones. Costs are saved by avoiding repeatedly transporting and processing the heavier recycled oligomerate.

BACKGROUND

When oligomerizing light olefins within a refinery, there is frequentlya desire to have the flexibility to make high octane gasoline, highcetane diesel, or combination of both. However, catalysts that make highoctane gasoline typically make product that is highly branched andwithin the gasoline boiling point range. This product is veryundesirable for diesel. In addition, catalysts that make high cetanediesel typically make product that is more linear and in the distillateboiling point range. This results in less and poorer quality gasolinedue to the more linear nature of the product which has a lower octanevalue.

The oligomerization of butenes is often associated with a desire to makea high yield of high quality gasoline product. There is typically alimit as to what can be achieved when oligomerizing butenes. Whenoligomerizing butenes, dimerization is desired to obtain gasoline rangematerial. However, trimerization and higher oligomerization can occurwhich can produce material heavier than gasoline such as diesel. Effortsto produce diesel by oligomerization have failed to provide high yieldsexcept through multiple passes.

When oligomerizing olefins from a fluid catalytic cracking (FCC) unit,there is often a desire to maintain a liquid phase within theoligomerization reactors. A liquid phase helps with catalyst stabilityby acting as a solvent to wash the catalyst of heavier species produced.In addition, the liquid phase provides a higher concentration of olefinsto the catalyst surface to achieve a higher catalyst activity. Thisliquid phase in the reactor may be maintained by recycling heavyoligomerate to the oligomerization reactor.

To maximize propylene produced by the FCC unit, refiners may contemplateoligomerizing FCC olefins to make heavy oligomerate and recycling heavyoligomers to the FCC unit for cracking down to propylene.

Recycling heavy oligomers to the oligomerization unit or the FCC unitrequires the heavy oligomers to be separated from lighter hydrocarbonsin the oligomerate effluent typically in a fractionation column. Arecycle ratio of oligomerate to feed can exceed 1. Transporting andseparating heavy oligomerate recycled to the fractionation column exactshigh utility costs.

Efficient processes and apparatuses are desired to recycle heavyoligomerate.

SUMMARY

We have discovered a process and apparatus that uses a flash drum toinitially separate heavy oligomerate from light oligomerate, so thelight oligomerate can bypass a fractionation column in an oligomeraterecovery section. Operational expenses for separating heavy oligomeratefrom light oligomerate are reduced because the heavy oligomerate whichis more utility intensive to transport and separate is decreased.

An embodiment is a process for making oligomers comprising passing anoligomerization feed stream to an oligomerization zone to oligomerizeolefins in the oligomerization feed stream to produce an oligomeratestream; separating the oligomerate stream from the oligomerization zonein a flash drum to provide a light flash oligomerate stream and a heavyflash oligomerate stream; fractionating the light flash oligomeratestream in a recovery zone; and recycling at least a portion of the heavyflash oligomerate stream to the oligomerization zone.

An embodiment is an apparatus for making oligomers comprising anoligomerization zone for oligomerizing olefins in the oligomerizationfeed stream to produce an oligomerate stream; a flash drum forseparating the oligomerate stream in communication with theoligomerization zone. a light flash line from the flash drum and a heavyflash line from the flash drum with an inlet to the light flash lineabove an inlet to the heavy flash line; a fractionation column incommunication with the light flash line for fractionating the lightflash oligomerate stream; and the oligomerization zone in downstreamcommunication with the heavy flash line.

An object is to recycle heavy oligomerate to oligomerization or fluidcatalytic cracking at lower expense.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing of the present invention.

FIG. 2 is a plot of C₈-C₁₁ olefin selectivity versus normal buteneconversion.

FIG. 3 is a plot of C₁₂₊ olefin selectivity versus normal buteneconversion.

FIG. 4 is a plot of reactant conversion versus total butene conversion.

FIG. 5 is a plot of normal butene conversion versus reactor temperature.

FIGS. 6 and 7 are plots of butene conversion versus total buteneconversion.

FIG. 8 is a plot of selectivity versus maximum reactor bed temperature.

FIGS. 9-11 are bar graphs of conversion and yield for three differentcatalysts.

FIG. 12 is a plot of C₃ olefin yield versus VGO conversion.

DEFINITIONS

As used herein, the term “stream” can include various hydrocarbonmolecules and other substances. Moreover, the term “stream comprisingC_(x) hydrocarbons” or “stream comprising C_(x) olefins” can include astream comprising hydrocarbon or olefin molecules, respectively, with“x” number of carbon atoms, suitably a stream with a majority ofhydrocarbons or olefins, respectively, with “x” number of carbon atomsand preferably a stream with at least 75 wt % hydrocarbons or olefinmolecules, respectively, with “x” number of carbon atoms. Moreover, theterm “stream comprising C_(x)+ hydrocarbons” or “stream comprisingC_(x)+ olefins” can include a stream comprising a majority ofhydrocarbon or olefin molecules, respectively, with more than or equalto “x” carbon atoms and suitably less than 10 wt % and preferably lessthan 1 wt % hydrocarbon or olefin molecules, respectively, with x−1carbon atoms. Lastly, the term “C_(x)− stream” can include a streamcomprising a majority of hydrocarbon or olefin molecules, respectively,with less than or equal to “x” carbon atoms and suitably less than 10 wt% and preferably less than 1 wt % hydrocarbon or olefin molecules,respectively, with x+1 carbon atoms.

As used herein, the term “zone” can refer to an area including one ormore equipment items and/or one or more sub-zones. Equipment items caninclude one or more reactors or reactor vessels, heaters, exchangers,pipes, pumps, compressors, controllers and columns. Additionally, anequipment item, such as a reactor, dryer, or vessel, can further includeone or more zones or sub-zones.

As used herein, the term “substantially” can mean an amount of at leastgenerally about 70%, preferably about 80%, and optimally about 90%, byweight, of a compound or class of compounds in a stream.

As used herein, the term “gasoline” can include hydrocarbons having aboiling point temperature in the range of about 25° to about 200° C. atatmospheric pressure.

As used herein, the term “diesel” or “distillate” can includehydrocarbons having a boiling point temperature in the range of about150° to about 400° C. and preferably about 200° to about 400° C.

As used herein, the term “vacuum gas oil” (VGO) can include hydrocarbonshaving a boiling temperature in the range of from 343° to 552° C.

As used herein, the term “vapor” can mean a gas or a dispersion that mayinclude or consist of one or more hydrocarbons.

As used herein, the term “overhead stream” can mean a stream withdrawnat or near a top of a vessel, such as a column.

As used herein, the term “bottom stream” can mean a stream withdrawn ator near a bottom of a vessel, such as a column.

As depicted, process flow lines in the figures can be referred tointerchangeably as, e.g., lines, pipes, feeds, gases, products,discharges, parts, portions, or streams.

As used herein, “bypassing” with respect to a vessel or zone means thata stream does not pass through the zone or vessel bypassed although itmay pass through a vessel or zone that is not designated as bypassed.

The term “communication” means that material flow is operativelypermitted between enumerated components.

The term “downstream communication” means that at least a portion ofmaterial flowing to the subject in downstream communication mayoperatively flow from the object with which it communicates.

The term “upstream communication” means that at least a portion of thematerial flowing from the subject in upstream communication mayoperatively flow to the object with which it communicates.

The term “direct communication” means that flow from the upstreamcomponent enters the downstream component without undergoing acompositional change due to physical fractionation or chemicalconversion.

The term “column” means a distillation column or columns for separatingone or more components of different volatilities. Unless otherwiseindicated, each column includes a condenser on an overhead of the columnto condense and reflux a portion of an overhead stream back to the topof the column and a reboiler at a bottom of the column to vaporize andsend a portion of a bottom stream back to the bottom of the column.Feeds to the columns may be preheated. The top pressure is the pressureof the overhead vapor at the outlet of the column. The bottomtemperature is the liquid bottom outlet temperature. Overhead lines andbottom lines refer to the net lines from the column downstream of thereflux or reboil to the column.

As used herein, the term “boiling point temperature” means atmosphericequivalent boiling point (AEBP) as calculated from the observed boilingtemperature and the distillation pressure, as calculated using theequations furnished in ASTM D1160 appendix A7 entitled “Practice forConverting Observed Vapor Temperatures to Atmospheric EquivalentTemperatures”.

As used herein, “taking a stream from” means that some or all of theoriginal stream is taken.

DETAILED DESCRIPTION

The present invention is an apparatus and process that can be used tomake gasoline, diesel and propylene. The apparatus and process may bedescribed with reference to five components shown in FIG. 1: a fluidcatalytic cracking (FCC) zone 20, an FCC recovery zone 100, apurification zone 110, an oligomerization zone 130, and anoligomerization recovery zone 200. Many configurations of the presentinvention are possible, but specific embodiments are presented herein byway of example. All other possible embodiments for carrying out thepresent invention are considered within the scope of the presentinvention.

The FCC zone 20 may comprise a first FCC reactor 22, a regeneratorvessel 30, and an optional second FCC reactor 70.

A conventional FCC feedstock and higher boiling hydrocarbon feedstockare a suitable FCC hydrocarbon feed 24 to the first FCC reactor. Themost common of such conventional feedstocks is a VGO. Higher boilinghydrocarbon feedstocks to which this invention may be applied includeheavy bottom from crude oil, heavy bitumen crude oil, shale oil, tarsand extract, deasphalted residue, products from coal liquefaction,atmospheric and vacuum reduced crudes and mixtures thereof. The FCC feed24 may include an FCC recycle stream from FCC recycle line 280 to bedescribed later.

The first FCC reactor 22 may include a first reactor riser 26 and afirst reactor vessel 28. A regenerator catalyst pipe 32 deliversregenerated catalyst from the regenerator vessel 30 to the reactor riser26. A fluidization medium such as steam from a distributor 34 urges astream of regenerated catalyst upwardly through the first reactor riser26. At least one feed distributor injects the first hydrocarbon feed ina first hydrocarbon feed line 24, preferably with an inert atomizing gassuch as steam, across the flowing stream of catalyst particles todistribute hydrocarbon feed to the first reactor riser 26. Uponcontacting the hydrocarbon feed with catalyst in the first reactor riser26 the heavier hydrocarbon feed cracks to produce lighter gaseouscracked products while coke is deposited on the catalyst particles toproduce spent catalyst.

The resulting mixture of gaseous product hydrocarbons and spent catalystcontinues upwardly through the first reactor riser 26 and are receivedin the first reactor vessel 28 in which the spent catalyst and gaseousproduct are separated. Disengaging arms discharge the mixture of gas andcatalyst from a top of the first reactor riser 26 through outlet ports36 into a disengaging vessel 38 that effects partial separation of gasesfrom the catalyst. A transport conduit carries the hydrocarbon vapors,stripping media and entrained catalyst to one or more cyclones 42 in thefirst reactor vessel 28 which separates spent catalyst from thehydrocarbon gaseous product stream. Gas conduits deliver separatedhydrocarbon cracked gaseous streams from the cyclones 42 to a collectionplenum 44 for passage of a cracked product stream to a first crackedproduct line 46 via an outlet nozzle and eventually into the FCCrecovery zone 100 for product recovery.

Diplegs discharge catalyst from the cyclones 42 into a lower bed in thefirst reactor vessel 28. The catalyst with adsorbed or entrainedhydrocarbons may eventually pass from the lower bed into a strippingsection 48 across ports defined in a wall of the disengaging vessel 38.Catalyst separated in the disengaging vessel 38 may pass directly intothe stripping section 48 via a bed. A fluidizing distributor deliversinert fluidizing gas, typically steam, to the stripping section 48. Thestripping section 48 contains baffles or other equipment to promotecontacting between a stripping gas and the catalyst. The stripped spentcatalyst leaves the stripping section 48 of the disengaging vessel 38 ofthe first reactor vessel 28 stripped of hydrocarbons. A first portion ofthe spent catalyst, preferably stripped, leaves the disengaging vessel38 of the first reactor vessel 28 through a spent catalyst conduit 50and passes into the regenerator vessel 30. A second portion of the spentcatalyst may be recirculated in recycle conduit 52 from the disengagingvessel 38 back to a base of the first riser 26 at a rate regulated by aslide valve to recontact the feed without undergoing regeneration.

The first riser 26 can operate at any suitable temperature, andtypically operates at a temperature of about 150° to about 580° C. atthe riser outlet 36. The pressure of the first riser is from about 69 toabout 517 kPa (gauge) (10 to 75 psig) but typically less than about 275kPa (gauge) (40 psig). The catalyst-to-oil ratio, based on the weight ofcatalyst and feed hydrocarbons entering the riser, may range up to 30:1but is typically between about 4:1 and about 25:1. Steam may be passedinto the first reactor riser 26 and first reactor vessel 28 at a ratebetween about 2 and about 7 wt % for maximum gasoline production andabout 10 to about 30 wt % for maximum light olefin production. Theaverage residence time of catalyst in the riser may be less than about 5seconds.

The catalyst in the first reactor 22 can be a single catalyst or amixture of different catalysts. Usually, the catalyst includes twocatalysts, namely a first FCC catalyst, and a second FCC catalyst. Sucha catalyst mixture is disclosed in, e.g., U.S. Pat. No. 7,312,370 B2.Generally, the first FCC catalyst may include any of the well-knowncatalysts that are used in the art of FCC. Preferably, the first FCCcatalyst includes a large pore zeolite, such as a Y-type zeolite, anactive alumina material, a binder material, including either silica oralumina, and an inert filler such as kaolin.

Typically, the zeolites appropriate for the first FCC catalyst have alarge average pore size, usually with openings of greater than about 0.7nm in effective diameter defined by greater than about 10, and typicallyabout 12, member rings. Suitable large pore zeolite components mayinclude synthetic zeolites such as X and Y zeolites, mordenite andfaujasite. A portion of the first FCC catalyst, such as the zeoliteportion, can have any suitable amount of a rare earth metal or rareearth metal oxide.

The second FCC catalyst may include a medium or smaller pore zeolitecatalyst, such as exemplified by at least one of ZSM-5, ZSM-11, ZSM-12,ZSM-23, ZSM-35, ZSM-38, ZSM-48, and other similar materials. Othersuitable medium or smaller pore zeolites include ferrierite, anderionite. Preferably, the second component has the medium or smallerpore zeolite dispersed on a matrix including a binder material such assilica or alumina and an inert filler material such as kaolin. Thesecatalysts may have a crystalline zeolite content of about 10 to about 50wt % or more, and a matrix material content of about 50 to about 90 wt%. Catalysts containing at least about 40 wt % crystalline zeolitematerial are typical, and those with greater crystalline zeolite contentmay be used. Generally, medium and smaller pore zeolites arecharacterized by having an effective pore opening diameter of less thanor equal to about 0.7 nm and rings of about 10 or fewer members.Preferably, the second FCC catalyst component is an MFI zeolite having asilicon-to-aluminum ratio greater than about 15. In one exemplaryembodiment, the silicon-to-aluminum ratio can be about 15 to about 35.

The total catalyst mixture in the first reactor 22 may contain about 1to about 25 wt % of the second FCC catalyst, including a medium to smallpore crystalline zeolite, with greater than or equal to about 7 wt % ofthe second FCC catalyst being preferred. When the second FCC catalystcontains about 40 wt % crystalline zeolite with the balance being abinder material, an inert filler, such as kaolin, and optionally anactive alumina component, the catalyst mixture may contain about 0.4 toabout 10 wt % of the medium to small pore crystalline zeolite with apreferred content of at least about 2.8 wt %. The first FCC catalyst maycomprise the balance of the catalyst composition. The high concentrationof the medium or smaller pore zeolite as the second FCC catalyst of thecatalyst mixture can improve selectivity to light olefins. In oneexemplary embodiment, the second FCC catalyst can be a ZSM-5 zeolite andthe catalyst mixture can include about 0.4 to about 10 wt % ZSM-5zeolite excluding any other components, such as binder and/or filler.

The regenerator vessel 30 is in downstream communication with the firstreactor vessel 28. In the regenerator vessel 30, coke is combusted fromthe portion of spent catalyst delivered to the regenerator vessel 30 bycontact with an oxygen-containing gas such as air to regenerate thecatalyst. The spent catalyst conduit 50 feeds spent catalyst to theregenerator vessel 30. The spent catalyst from the first reactor vessel28 usually contains carbon in an amount of from 0.2 to 7 wt %, which ispresent in the form of coke. An oxygen-containing combustion gas,typically air, enters the lower chamber 54 of the regenerator vessel 30through a conduit and is distributed by a distributor 56. As thecombustion gas enters the lower chamber 54, it contacts spent catalystentering from spent catalyst conduit 50 and lifts the catalyst at asuperficial velocity of combustion gas in the lower chamber 54 ofperhaps at least 1.1 m/s (3.5 ft/s) under fast fluidized flowconditions. In an embodiment, the lower chamber 54 may have a catalystdensity of from 48 to 320 kg/m³ (3 to 20 lb/ft³) and a superficial gasvelocity of 1.1 to 2.2 m/s (3.5 to 7 ft/s). The oxygen in the combustiongas contacts the spent catalyst and combusts carbonaceous deposits fromthe catalyst to at least partially regenerate the catalyst and generateflue gas.

The mixture of catalyst and combustion gas in the lower chamber 54ascends through a frustoconical transition section to the transport,riser section of the lower chamber 54. The mixture of catalyst particlesand flue gas is discharged from an upper portion of the riser sectioninto the upper chamber 60. Substantially completely or partiallyregenerated catalyst may exit the top of the transport, riser section.Discharge is effected through a disengaging device 58 that separates amajority of the regenerated catalyst from the flue gas. The catalyst andgas exit downwardly from the disengaging device 58. The sudden loss ofmomentum and downward flow reversal cause a majority of the heaviercatalyst to fall to the dense catalyst bed and the lighter flue gas anda minor portion of the catalyst still entrained therein to ascendupwardly in the upper chamber 60. Cyclones 62 further separate catalystfrom ascending gas and deposits catalyst through dip legs into a densecatalyst bed. Flue gas exits the cyclones 62 through a gas conduit andcollects in a plenum 64 for passage to an outlet nozzle of regeneratorvessel 30. Catalyst densities in the dense catalyst bed are typicallykept within a range of from about 640 to about 960 kg/m³ (40 to 60lb/ft³).

The regenerator vessel 30 typically has a temperature of about 594° toabout 704° C. (1100° to 1300° F.) in the lower chamber 54 and about 649°to about 760° C. (1200° to 1400° F.) in the upper chamber 60.Regenerated catalyst from dense catalyst bed is transported throughregenerated catalyst pipe 32 from the regenerator vessel 30 back to thefirst reactor riser 26 through the control valve where it again contactsthe first feed in line 24 as the FCC process continues. The firstcracked product stream in the first cracked product line 46 from thefirst reactor 22, relatively free of catalyst particles and includingthe stripping fluid, exit the first reactor vessel 28 through an outletnozzle. The first cracked products stream in the line 46 may besubjected to additional treatment to remove fine catalyst particles orto further prepare the stream prior to fractionation. The line 46transfers the first cracked products stream to the FCC recovery zone100, which is in downstream communication with the FCC zone 20.

The FCC recovery zone 100 typically includes a main fractionation columnand a gas recovery section. The FCC recovery zone can include manyfractionation columns and other separation equipment. The FCC recoveryzone 100 can recover a propylene product stream in propylene line 102, agasoline stream in gasoline line 104, a light olefin stream in lightolefin line 106 and an LCO stream in LCO line 107 among others from thecracked product stream in first cracked product line 46. The lightolefin stream in light olefin line 106 comprises an oligomerization feedstream having C₄ hydrocarbons including C₄ olefins and perhaps having C₅hydrocarbons including C₅ olefins.

An FCC recycle line 280 delivers an FCC recycle stream to the FCC zone20. The FCC recycle stream is directed into a first FCC recycle line 202with the control valve 202′ thereon opened. In an aspect, the FCCrecycle stream may be directed into an optional second FCC recycle line204 with the control valve 204′ thereon opened. The first FCC recycleline 202 delivers the first FCC recycle stream to the first FCC reactor22 in an aspect to the riser 26 at an elevation above the firsthydrocarbon feed in line 24. The second FCC recycle line 204 deliversthe second FCC recycle stream to the second FCC reactor 70. Typically,both control valves 202′ and 204′ will not be opened at the same time,so the FCC recycle stream goes through only one of the first FCC recycleline 202 and the second FCC recycle line 204. However, feed through bothis contemplated.

The second FCC recycle stream may be fed to the second FCC reactor 70 inthe second FCC recycle line 204 via feed distributor 72. The second FCCreactor 70 may include a second riser 74. The second FCC recycle streamis contacted with catalyst delivered to the second riser 74 by acatalyst return pipe 76 to produce cracked upgraded products. Thecatalyst may be fluidized by inert gas such as steam from distributor78. Generally, the second FCC reactor 70 may operate under conditions toconvert the second FCC recycle stream to second cracked products such asethylene and propylene. A second reactor vessel 80 is in downstreamcommunication with the second riser 74 for receiving second crackedproducts and catalyst from the second riser. The mixture of gaseous,second cracked product hydrocarbons and catalyst continues upwardlythrough the second reactor riser 74 and is received in the secondreactor vessel 80 in which the catalyst and gaseous, second crackedproducts are separated. A pair of disengaging arms may tangentially andhorizontally discharge the mixture of gas and catalyst from a top of thesecond reactor riser 74 through one or more outlet ports 82 (only one isshown) into the second reactor vessel 80 that effects partial separationof gases from the catalyst. The catalyst can drop to a dense catalystbed within the second reactor vessel 80. Cyclones 84 in the secondreactor vessel 80 may further separate catalyst from second crackedproducts. Afterwards, a second cracked product stream can be removedfrom the second FCC reactor 70 through an outlet in a second crackedproduct line 86 in downstream communication with the second reactorriser 74. The second cracked product stream in line 86 is fed to the FCCrecovery zone 100, preferably separately from the first cracked productsto undergo separation and recovery of ethylene and propylene. Separatedcatalyst may be recycled via a recycle catalyst pipe 76 from the secondreactor vessel 80 regulated by a control valve back to the secondreactor riser 74 to be contacted with the second FCC recycle stream.

In some embodiments, the second FCC reactor 70 can contain a mixture ofthe first and second FCC catalysts as described above for the first FCCreactor 22. In one preferred embodiment, the second FCC reactor 70 cancontain less than about 20 wt %, preferably less than about 5 wt % ofthe first FCC catalyst and at least 20 wt % of the second FCC catalyst.In another preferred embodiment, the second FCC reactor 70 can containonly the second FCC catalyst, preferably a ZSM-5 zeolite.

The second FCC reactor 70 is in downstream communication with theregenerator vessel 30 and receives regenerated catalyst therefrom inline 88. In an embodiment, the first FCC reactor 22 and the second FCCreactor 70 both share the same regenerator vessel 30. Line 90 carriesspent catalyst from the second reactor vessel 80 to the lower chamber 54of the regenerator vessel 30. The catalyst regenerator is in downstreamcommunication with the second FCC reactor 70 via line 90.

The same catalyst composition may be used in both reactors 22, 70.However, if a higher proportion of the second FCC catalyst of small tomedium pore zeolite is desired in the second FCC reactor 70 than thefirst FCC catalyst of large pore zeolite, replacement catalyst added tothe second FCC reactor 70 may comprise a higher proportion of the secondFCC catalyst. Because the second FCC catalyst does not lose activity asquickly as the first FCC catalyst, less of the second catalyst inventorymust be forwarded to the catalyst regenerator 30 in line 90 from thesecond reactor vessel 80, but more catalyst inventory may be recycled tothe riser 74 in return conduit 76 without regeneration to maintain ahigh level of the second FCC catalyst in the second reactor 70.

The second reactor riser 74 can operate in any suitable condition, suchas a temperature of about 425° to about 705° C., preferably atemperature of about 550° to about 600° C., and a pressure of about 140to about 400 kPa, preferably a pressure of about 170 to about 250 kPa.Typically, the residence time of the second reactor riser 74 can be lessthan about 3 seconds and preferably is less than about 1 second.Exemplary risers and operating conditions are disclosed in, e.g., US2008/0035527 A1 and U.S. Pat. No. 7,261,807 B2.

Before cracked products can be fed to the oligomerization zone 130, thelight olefin stream in light olefin line 106 may require purification.Many impurities in the light olefin stream in light olefin line 106 canpoison an oligomerization catalyst. Carbon dioxide and ammonia canattack acid sites on the catalyst. Sulfur containing compounds,oxygenates, and nitriles can harm oligomerization catalyst. Acetylenesand diolefins can polymerize and produce gums on the catalyst orequipment. Consequently, the light olefin stream which comprises theoligomerization feed stream in light olefin line 106 may be purified inan optional purification zone 110.

The light olefin stream in light olefin line 106 may be introduced intoan optional mercaptan extraction unit 112 to remove mercaptans to lowerconcentrations. In the mercaptan extraction unit 112, the light olefinfeed may be prewashed in an optional prewash vessel containing aqueousalkali to convert any hydrogen sulfide to sulfide salt which is solublein the aqueous alkaline stream. The light olefin stream, now depleted ofany hydrogen sulfide, is contacted with a more concentrated aqueousalkali stream in an extractor vessel. Mercaptans in the light olefinstream react with the alkali to yield mercaptides. An extracted lightolefin stream lean in mercaptans passes overhead from the extractioncolumn and may be mixed with a solvent that removes COS in route to anoptional COS solvent settler. COS may be removed with the solvent fromthe bottom of the settler, while the overhead light olefin stream may befed to an optional water wash vessel to remove remaining alkali andproduce a sulfur depleted light olefin stream in line 114. Themercaptide rich alkali from the extractor vessel receives an injectionof air and a catalyst such as phthalocyanine as it passes from theextractor vessel to an oxidation vessel for regeneration. Oxidizing themercaptides to disulfides using a catalyst regenerates the alkalinesolution. A disulfide separator receives the disulfide rich alkalinefrom the oxidation vessel. The disulfide separator vents excess air anddecants disulfides from the alkaline solution before the regeneratedalkaline is drained, washed with oil to remove remaining disulfides andreturned to the extractor vessel. Further removal of disulfides from theregenerated alkaline stream is also contemplated. The disulfides may berun through a sand filter and removed from the process. For moreinformation on mercaptan extraction, reference may be made to U.S. Pat.No. 7,326,333 B2.

In order to prevent polymerization and gumming in the oligomerizationreactor that can inhibit equipment and catalyst performance, it isdesired to minimize diolefins and acetylenes in the light olefin feed inline 114. Diolefin conversion to monoolefin hydrocarbons may beaccomplished by selectively hydrogenating the sulfur depleted streamwith a conventional selective hydrogenation reactor 116. Hydrogen may beadded to the purified light olefin stream in line 118.

The selective hydrogenation catalyst can comprise an alumina supportmaterial preferably having a total surface area greater than 150 m²/g,with most of the total pore volume of the catalyst provided by poreswith average diameters of greater than 600 angstroms, and containingsurface deposits of about 1.0 to 25.0 wt % nickel and about 0.1 to 1.0wt % sulfur such as disclosed in U.S. Pat. No. 4,695,560. Spheres havinga diameter between about 0.4 and 6.4 mm ( 1/64 and ¼ inch) can be madeby oil dropping a gelled alumina sol. The alumina sol may be formed bydigesting aluminum metal with an aqueous solution of approximately 12 wt% hydrogen chloride to produce an aluminum chloride sol. The nickelcomponent may be added to the catalyst during the sphere formation or byimmersing calcined alumina spheres in an aqueous solution of a nickelcompound followed by drying, calcining, purging and reducing. The nickelcontaining alumina spheres may then be sulfided. A palladium catalystmay also be used as the selective hydrogenation catalyst.

The selective hydrogenation process is normally performed at relativelymild hydrogenation conditions. These conditions will normally result inthe hydrocarbons being present as liquid phase materials. The reactantswill normally be maintained under the minimum pressure sufficient tomaintain the reactants as liquid phase hydrocarbons which allow thehydrogen to dissolve into the light olefin feed. A broad range ofsuitable operating pressures therefore extends from about 276 (40 psig)to about 5516 kPa gauge (800 psig). A relatively moderate temperaturebetween about 25° C. (77° F.) and about 350° C. (662° F.) should beemployed. The liquid hourly space velocity of the reactants through theselective hydrogenation catalyst should be above 1.0 hr⁻¹. Preferably,it is between 5.0 and 35.0 hr⁻¹. The molar ratio of hydrogen todiolefinic hydrocarbons may be maintained between 1.5:1 and 2:1. Thehydrogenation reactor is preferably a cylindrical fixed bed of catalystthrough which the reactants move in a vertical direction.

A purified light olefin stream depleted of sulfur containing compounds,diolefins and acetylenes exits the selective hydrogenation reactor 116in line 120. The optionally sulfur and diolefin depleted light olefinstream in line 120 may be introduced into an optional nitrile removalunit (NRU) such as a water wash unit 122 to reduce the concentration ofoxygenates and nitriles in the light olefin stream in line 120. Water isintroduced to the water wash unit in line 124. An oxygenate andnitrile-rich aqueous stream in line 126 leaves the water wash unit 122and may be further processed. A drier may follow the water wash unit122. Other NRU's may be used in place of the water wash unit. A NRU canconsist of a group of regenerable beds that adsorb the nitriles andother nitrogen components from the diolefin depleted light olefinstream. Examples of NRU's can be found in U.S. Pat. No. 4,831,206, U.S.Pat. No. 5,120,881 and U.S. Pat. No. 5,271,835.

A purified light olefin oligomerization feed stream perhaps depleted ofsulfur containing compounds, diolefins and/or oxygenates and nitriles isprovided in oligomerization feed stream line 128. The light olefinoligomerization feed stream in line 128 may be obtained from the crackedproduct stream in lines 46 and/or 86, so it may be in downstreamcommunication with the FCC zone 20 and/or the FCC recovery zone 100. Theoligomerization feed stream need not be obtained from a cracked FCCproduct stream but may come from another source such as from a paraffindehydrogenation unit or a unit that converts oxygenates to olefins. Theselective hydrogenation reactor 116 is in upstream communication withthe oligomerization feed stream line 128. The oligomerization feedstream may comprise C₄ hydrocarbons such as butenes, i.e., C₄ olefins,and butanes. Butenes include normal butenes and isobutene. Theoligomerization feed stream in oligomerization feed stream line 128 maycomprise C₅ hydrocarbons such as pentenes, i.e., C₅ olefins, andpentanes. Pentenes include normal pentenes and isopentenes. Typically,the oligomerization feed stream will comprise about 20 to about 80 wt %olefins and suitably about 40 to about 75 wt % olefins. In an aspect,about 55 to about 75 wt % of the olefins may be butenes and about 25 toabout 45 wt % of the olefins may be pentenes. Up to as much as 10 wt %,suitably 20 wt %, typically 25 wt % and most typically 30 wt % of theoligomerization feed may be C₅ olefins.

The oligomerization feed line 128 feeds the oligomerization feed streamto an oligomerization zone 130 which may be in downstream communicationwith the FCC recovery zone 100. The oligomerization feed stream inoligomerization feed line 128 may be mixed with recycle streams fromline 225, 226 or 230 prior to entering the oligomerization zone 130 toprovide a mixed oligomerization feed stream in a mixed oligomerizationfeed conduit 132. An oligomerization zone 130 is in downstreamcommunication with the mixed oligomerization feed conduit 132. The ratioof recycle oligomerate from lines 225, 226 and 230 to theoligomerization feed from line 128 in the mixed oligomerization feedconduit 132 is about 1:1 to about 5:1.

In an aspect, an oligomerate recycle stream in oligomerate recycle line230 to be described hereinafter may be mixed with the oligomerizationfeed stream in the oligomerization feed conduit line 128. Theoligomerization feed stream in the oligomerization feed conduit 132 maycomprise about 10 to about 50 wt % olefins and suitably about 25 toabout 40 wt % olefins if the oligomerate recycle stream from oligomeratereturn line 230 is mixed with the oligomerization feed stream.Accordingly, the oligomerization feed stream may comprise no more thanabout 38 wt % butene and in another aspect, the oligomerization feedstream may comprise no more than about 23 wt % pentene. Theoligomerization feed stream to the oligomerization zone 130 in mixedoligomerization feed conduit 132 may comprise at least about 10 wt %butene, at least about 5 wt % pentene and preferably no more than about1 wt % hexene. In a further aspect, the oligomerization feed stream maycomprise no more than about 0.1 wt % hexene and no more than about 0.1wt % propylene. At least about 40 wt % of the butene in theoligomerization feed stream may be normal butene. In an aspect, it maybe that no more than about 70 wt % of the oligomerization feed stream isnormal butene. At least about 40 wt % of the pentene in theoligomerization feed stream may be normal pentene. In an aspect, no morethan about 70 wt % of the oligomerization feed stream in the mixedoligomerization feed conduit 132 may be normal pentene.

The oligomerization zone 130 comprises a first oligomerization reactor138. The first oligomerization reactor may be preceded by an optionalguard bed for removing catalyst poisons that is not shown. The firstoligomerization reactor 138 contains the oligomerization catalyst. Anoligomerization feed stream may be preheated before entering the firstoligomerization reactor 138 in an oligomerization zone 130. The firstoligomerization reactor 138 may contain a first catalyst bed 142 ofoligomerization catalyst. The first oligomerization reactor 138 may bean upflow reactor to provide a uniform feed front through the catalystbed, but other flow arrangements are contemplated. In an aspect, thefirst oligomerization reactor 138 may contain an additional bed or beds144 of oligomerization catalyst. C₄ olefins in the oligomerization feedstream oligomerize over the oligomerization catalyst to provide anoligomerate comprising C₄ olefin dimers and trimers. C₅ olefins that maybe present in the oligomerization feed stream oligomerize over theoligomerization catalyst to provide an oligomerate comprising C₅ olefindimers and trimers and co-oligomerize with C₄ olefins to make C₉olefins. The oligomerization produces other oligomers with additionalcarbon numbers.

Oligomerization effluent from the first bed 142 may optionally bequenched with a liquid such as recycled oligomerate before entering theadditional bed 144, and/or oligomerization effluent from the additionalbed 144 of oligomerization catalyst may also be quenched with a liquidsuch as recycled oligomerate to avoid excessive temperature rise. Theliquid oligomerate may also comprise oligomerized olefins that can reactwith the C₄ olefins and C₅ olefins in the feed and other oligomerizedolefins if present to make diesel range olefins. Oligomerized product,also known as oligomerate, exits the first oligomerization reactor 138in line 146.

In an aspect, the oligomerization reactor zone may include one or moreadditional oligomerization reactors 150. The oligomerization effluentmay be heated and fed to the optional additional oligomerization reactor150. It is contemplated that the first oligomerization reactor 138 andthe additional oligomerization reactor 150 may be operated in a swingbed fashion to take one reactor offline for maintenance or catalystregeneration or replacement while the other reactor stays online. In anaspect, the additional oligomerization reactor 150 may contain a firstbed 152 of oligomerization catalyst. The additional oligomerizationreactor 150 may also be an upflow reactor to provide a uniform feedfront through the catalyst bed, but other flow arrangements arecontemplated. In an aspect, the additional oligomerization reactor 150may contain an additional bed or beds 154 of oligomerization catalyst.Remaining C₄ olefins in the oligomerization feed stream oligomerize overthe oligomerization catalyst to provide an oligomerate comprising C₄olefin dimers and trimers. Remaining C₅ olefins, if present in theoligomerization feed stream, oligomerize over the oligomerizationcatalyst to provide an oligomerate comprising C₅ olefin dimers andtrimers and co-oligomerize with C₄ olefins to make C₉ olefins. Over 90wt % of the C₄ olefins in the oligomerization feed stream canoligomerize in the oligomerization zone 130. Over 90 wt % of the C₅olefins in the oligomerization feed stream can oligomerize in theoligomerization zone 130. If more than one oligomerization reactor isused, conversion is achieved over all of the oligomerization reactors138, 150 in the oligomerization zone 130.

Oligomerization effluent from the first bed 152 may be quenched with aliquid such as recycled oligomerate before entering the additional bed154, and/or oligomerization effluent from the additional bed 154 ofoligomerization catalyst may also be quenched with a liquid such asrecycled oligomerate to avoid excessive temperature rise. The recycledoligomerate may also comprise oligomerized olefins that can react withthe C₄ olefins and C₅ olefins in the feed and other oligomerized olefinsto increase production of diesel range olefins.

An oligomerate conduit 156, in downstream communication with theoligomerization zone 130, withdraws an oligomerate stream from theoligomerization zone 130. The oligomerate conduit 156 may be indownstream communication with the first oligomerization reactor 138 andthe additional oligomerization reactor 150.

The oligomerization zone 130 may contain an oligomerization catalyst.The oligomerization catalyst may comprise a zeolitic catalyst. Thezeolite may comprise between 5 and 95 wt % of the catalyst. Suitablezeolites include zeolites having a structure from one of the followingclasses: MFI, MEL, SFV, SVR, ITH, IMF, TUN, FER, EUO, BEA, FAU, BPH,MEI, MSE, MWW, UZM-8, MOR, OFF, MTW, TON, MTT, AFO, ATO, and AEL. Thesethree-letter codes for structure types are assigned and maintained bythe International Zeolite Association Structure Commission in the Atlasof Zeolite Framework Types, which is athttp://www.iza-structure.org/databases/. In a preferred aspect, theoligomerization catalyst may comprise a zeolite with a framework havinga ten-ring pore structure. Examples of suitable zeolites having aten-ring pore structure include those comprising TON, MTT, MFI, MEL,AFO, AEL, EUO and FER. In a further preferred aspect, theoligomerization catalyst comprising a zeolite having a ten-ring porestructure may comprise a uni-dimensional pore structure. Auni-dimensional pore structure indicates zeolites containingnon-intersecting pores that are substantially parallel to one of theaxes of the crystal. The pores preferably extend through the zeolitecrystal. Suitable examples of zeolites having a ten-ring uni-dimensionalpore structure may include MTT. In a further aspect, the oligomerizationcatalyst comprises an MTT zeolite.

The oligomerization catalyst may be formed by combining the zeolite witha binder, and then forming the catalyst into pellets. The pellets mayoptionally be treated with a phosphoric reagent to create a zeolitehaving a phosphorous component between 0.5 and 15 wt % of the treatedcatalyst. The binder is used to confer hardness and strength on thecatalyst. Binders include alumina, aluminum phosphate, silica,silica-alumina, zirconia, titania and combinations of these metaloxides, and other refractory oxides, and clays such as montmorillonite,kaolin, palygorskite, smectite and attapulgite. A preferred binder is analuminum-based binder, such as alumina, aluminum phosphate,silica-alumina and clays.

One of the components of the catalyst binder utilized in the presentinvention is alumina. The alumina source may be any of the varioushydrous aluminum oxides or alumina gels such as alpha-aluminamonohydrate of the boehmite or pseudo-boehmite structure, alpha-aluminatrihydrate of the gibbsite structure, beta-alumina trihydrate of thebayerite structure, and the like. A suitable alumina is available fromUOP LLC under the trademark Versal. A preferred alumina is availablefrom Sasol North America Alumina Product Group under the trademarkCatapal. This material is an extremely high purity alpha-aluminamonohydrate (pseudo-boehmite) which after calcination at a hightemperature has been shown to yield a high purity gamma-alumina.

A suitable oligomerization catalyst is prepared by mixing proportionatevolumes of zeolite and alumina to achieve the desired zeolite-to-aluminaratio. In an embodiment, about 5 to about 80, typically about 10 toabout 60, suitably about 15 to about 40 and preferably about 20 to about30 wt % MTT zeolite and the balance alumina powder will provide asuitably supported catalyst. A silica support is also contemplated.

Monoprotic acid such as nitric acid or formic acid may be added to themixture in aqueous solution to peptize the alumina in the binder.Additional water may be added to the mixture to provide sufficientwetness to constitute a dough with sufficient consistency to be extrudedor spray dried. Extrusion aids such as cellulose ether powders can alsobe added. A preferred extrusion aid is available from The Dow ChemicalCompany under the trademark Methocel.

The paste or dough may be prepared in the form of shaped particulates,with the preferred method being to extrude the dough through a diehaving openings therein of desired size and shape, after which theextruded matter is broken into extrudates of desired length and dried. Afurther step of calcination may be employed to give added strength tothe extrudate. Generally, calcination is conducted in a stream of air ata temperature from about 260° C. (500° F.) to about 815° C. (1500° F.).The MTT catalyst is not selectivated to neutralize surface acid sitessuch as with an amine.

The extruded particles may have any suitable cross-sectional shape,i.e., symmetrical or asymmetrical, but most often have a symmetricalcross-sectional shape, preferably a spherical, cylindrical or polylobalshape. The cross-sectional diameter of the particles may be as small as40 μm; however, it is usually about 0.635 mm (0.25 inch) to about 12.7mm (0.5 inch), preferably about 0.79 mm ( 1/32 inch) to about 6.35 mm(0.25 inch), and most preferably about 0.06 mm ( 1/24 inch) to about4.23 mm (⅙ inch).

In an embodiment, the oligomerization catalyst may be a solid phosphoricacid catalyst (SPA). The SPA catalyst refers to a solid catalyst thatcontains as a principal ingredient an acid of phosphorous such asortho-, pyro- or tetraphosphoric acid. SPA catalyst is normally formedby mixing the acid of phosphorous with a siliceous solid carrier to forma wet paste. This paste may be calcined and then crushed to yieldcatalyst particles or the paste may be extruded or pelleted prior tocalcining to produce more uniform catalyst particles. The carrier ispreferably a naturally occurring porous silica-containing material suchas kieselguhr, kaolin, infusorial earth and diatomaceous earth. A minoramount of various additives such as mineral talc, fuller's earth andiron compounds including iron oxide may be added to the carrier toincrease its strength and hardness. The combination of the carrier andthe additives preferably comprises about 15-30 wt % of the catalyst,with the remainder being the phosphoric acid. The additive may compriseabout 3-20 wt % of the total carrier material. Variations from thiscomposition such as a lower phosphoric acid content are possible.Further details as to the composition and production of SPA catalystsmay be obtained from U.S. Pat. No. 3,050,472, U.S. Pat. No. 3,050,473and U.S. Pat. No. 3,132,109. Feed to the oligomerization zone 130containing SPA catalyst should be kept dry except in an initial start-upphase.

The oligomerization reaction conditions in the oligomerization reactors138, 150 in the oligomerization zone 130 are set to keep the reactantfluids in the liquid phase. With liquid oligomerate recycle, lowerpressures are necessary to maintain liquid phase. Operating pressuresinclude between about 2.1 MPa (300 psia) and about 10.5 MPa (1520 psia),suitably at a pressure between about 2.1 MPa (300 psia) and about 6.9MPa (1000 psia) and preferably at a pressure between about 2.8 MPa (400psia) and about 4.1 MPa (600 psia). Lower pressures may be suitable ifthe reaction is kept in the liquid phase.

For the zeolite catalyst, the temperature of the oligomerization zone130 expressed in terms of a maximum bed temperature is in a rangebetween about 150° and about 300° C. If diesel oligomerate is desired,the bed temperature should between about 200° and about 250° C. andpreferably between about 215° and about 245° C. or between about 220°and about 240° C. The weight hourly space velocity should be betweenabout 0.5 and about 5 hr⁻¹.

For the SPA catalyst, the oligomerization temperature in theoligomerization zone 130 should be in a range between about 100° andabout 250° C. and suitably between about 150° and about 200° C. Theweight hourly space velocity (LHSV) should be between about 0.5 andabout 5 hr⁻¹.

Across a single bed of oligomerization catalyst, the exothermic reactionwill cause the temperature to rise. Consequently, the oligomerizationreactor should be operated to allow the temperature at the outlet to beover about 25° C. greater than the temperature at the inlet.

The oligomerization zone 130 with the oligomerization catalyst can berun in high conversion mode of greater than 95% conversion of feedolefins to produce a high quality diesel product and gasoline product.Normal butene conversion can exceed about 80%. Additionally, normalpentene conversion can exceed about 80%.

We have found that when C₅ olefins are present in the oligomerizationfeed stream, they dimerize or co-dimerize with other olefins, but tendto mitigate further oligomerization over the zeolite with a 10-ringuni-dimensional pore structure. Best mitigation of furtheroligomerization occurs when the C₅ olefins comprise between about 15 andabout 50 wt % and preferably between 20 or 40 of the olefins in theoligomerization feed. Consequently, the oligomerate stream inoligomerate conduit 156 may comprise less than about 80 wt % C₉+hydrocarbons when C₅ olefins are present in the oligomerization feed atthese proportions. Moreover, said oligomerate may comprise less thanabout 60 wt % C₁₂+ hydrocarbons when C₅ olefins are present in theoligomerization feed at these proportions. Furthermore, the net gasolineyield may be at least about 40 wt % when C₅ olefins are present in theoligomerization feed.

If diesel is desired, however, the oligomerization zone with theoligomerization catalyst can be operated to oligomerize light olefins;i.e., C₄ olefins, to distillate-range material by over 70 wt % yield perpass through the oligomerization zone 130. In an aspect, at least about70 wt % of the olefins in the oligomerization feed convert to C₉+product oligomers boiling above about 150° C. (302° F.) cut point in asingle pass through the oligomerization zone. The C₁₂+ oligomer from theoligomerization zone boiling above about 200° C. (392° F.) may have acetane of at least 30 and preferably at least 40.

An oligomerization recovery zone 200 is in downstream communication withthe oligomerization zone 130 and the oligomerate conduit 156. Theoligomerate conduit 156 removes the oligomerate stream from theoligomerization zone 130.

In order to conduct an initial rough separation of a light streamcomprising unreacted olefins from a heavy oligomerate stream comprisinga C₆+ olefins, the oligomerate stream in the oligomerate conduit 156 maybe heat exchanged and then flashed in a flash drum 180 to provide alight flash stream in a flash overhead line 182 comprising C₄ andperhaps C₅ hydrocarbons and a heavy flash stream in a flash bottoms line184 comprising C₆+ olefinic hydrocarbons. The flash drum 180 is indownstream communication with the oligomerization zone 130. The lightflash line 182 from the flash drum 180 has an inlet 183 above an inlet185 to the heavy flash line 184. The light flash stream may befractionated in the oligomerization recovery zone 200 to provide aproduct stream while the heavy flash stream bypasses a debutanizercolumn 210 and/or a depentanizer column 220 in the oligomerizationrecovery zone 200. The temperature in the flash drum 180 may be betweenabout 138° C. (280° F.) and about 250° C. (482° F.) and the pressure maybe between about 2.8 MPa (gauge) (400 psig) and about 6.2 MPa (gauge)(900 psig).

The oligomerization recovery zone 200 may include a debutanizer column210 which is a fractionation column in downstream communication with thelight flash line 182. The debutanizer column 210 fractionates the lightflash oligomerate stream between vapor and liquid into a first vaporousoligomerate overhead light stream comprising C₄ olefins and hydrocarbonsin a first overhead line 212 and a first liquid oligomerate productstream comprising C₅+ olefins and hydrocarbons in a first product line214. The first product line 214 may come from the bottom of thedebutanizer column 210 and be a bottom line. When maximum production ofdistillate is desired, either to obtain diesel product or to recrack thediesel in the FCC zone 20 to make more propylene, the overhead pressurein the debutanizer column 210 may be between about 300 and about 700 kPa(gauge) and the bottom temperature may be between about 225° and about300° C. When maximum production of gasoline is desired, the overheadpressure in the debutanizer column 210 may be between about 300 andabout 700 kPa (gauge) and the bottom temperature may be between about175° and about 225° C.

The first liquid oligomerate product stream in the first product line214 may enter a surge drum via a route line 216 and a surge inlet line234. Some, all or none of the first liquid oligomerate product stream inthe first product line 214 may be routed through the route line 216 asregulated by a control valve 216′. If the oligomerization feed in theoligomerization feed line 128 does not include substantial C₅ olefins,the control valve 216′ may be fully open and a control valve 218′ on adepentanizer feed line 218 may be completely shut, so all of the firstliquid oligomerate product stream in the first product line 214 isrouted in the rout line 216. Consequently, the surge drum may be indownstream communication with the first product line 214.

If substantial C₅ olefins are in the oligomerization feed in theoligomerization feed line 128, the oligomerization recovery zone 200 mayinclude a depentanizer column 220. The depentanizer column 220 is afractionation column in downstream communication with the light flashline 182 and the first product line 214. The first liquid oligomerateproduct stream comprising C₅+ hydrocarbons may be fed in the firstproduct line 214 and the depentanizer feed line 218 to the depentanizercolumn 220. In such case, the control valve 218′ may be completely openand control valve 216′ may be completely shut, so all of the firstliquid oligomerate product stream in the first product line 214 is fedto the depentanizer column 220 in the depentanizer feed line 218.However, flow through both valves 216′ and 218′ is envisioned.

The depentanizer column 220 may be in downstream communication with thefirst product line 214 from said debutanizer column 210. Thedepentanizer column 220 may fractionate the first liquid oligomerateproduct stream in the first product line 214 between vapor and liquidinto an intermediate stream comprising C₅ olefins and hydrocarbons in anintermediate line 222 and a second liquid oligomerate product streamcomprising C₆+ olefins in a second product line 224. The second productline 224 may come from a bottom of the depentanizer column 220 and be abottom line. When maximum production of distillate is desired, either toobtain diesel product or to recrack the diesel in the FCC zone 20 tomake more propylene, the overhead pressure in the depentanizer column220 may be between about 50 and about 100 kPa (gauge) and the bottomtemperature may be between about 200° and about 275° C. When maximumproduction of gasoline is desired, the overhead pressure in thedepentanizer column 220 may be between about 100 and about 500 kPa(gauge) and the bottom temperature may be between about 150° and about225° C.

It is desired to maintain liquid phase in the oligomerization reactors.This can be achieved by saturating product olefins and recycling them tothe oligomerization reactor as a liquid. However, if olefinic product isbeing recycled to either the FCC zone 20 or the oligomerization zone130, saturating olefins would inactivate the recycle feed. Theoligomerization zone 130 can only further oligomerize olefinic recycleand the FCC zone 20 prefers olefinic feed to be further cracked to formpropylene. Liquid phase may be maintained in the first oligomerizationzone 130 by incorporating into the feed a C₄ stream and/or a C₅ streamfrom the oligomerization recovery zone 200.

The light stream in overhead line 212 may comprise at least 70 wt % andsuitably at least 90 wt % C₄ hydrocarbons which can be recycled ifincreased conversion of the light olefins is required. The overheadintermediate stream comprising C₄ hydrocarbons may have less than 10 wt% C₃ or C₅ hydrocarbons and preferably less than 1 wt % C₃ or C₅hydrocarbons.

The light stream in the overhead line 212 may be condensed and recycledto the first oligomerization zone 130 as a first light recycle stream ina light recycle line 225 at a rate governed by control valve 225′. Thelight stream may comprise C₄ olefins that can oligomerize in the firstoligomerization zone 130. The butanes are easily separated from theheavier olefinic product such as in the debutanizer column 210. Thebutane recycled to the oligomerization zone also dilutes the feedolefins to help limit the temperature rise within the oligomerizationreactor due to the exothermicity of the reaction.

In an aspect, the light stream in the overhead line 212 comprising C₄hydrocarbons may be split into a purge stream in purge line 229 and thelight recycle stream comprising C₄ hydrocarbons in the light recycleline 225. In an aspect, the light recycle stream in the light recycleline 225 taken from the light stream in the light line 212 is recycledto the first oligomerization zone 130 downstream of the selectivehydrogenation reactor 116. The light stream in the light line 212 andthe light recycle stream in the light recycle line 225 should beunderstood to be condensed overhead streams. The recycle rate may beadjusted as necessary to maximize selectivity to gasoline range oligomerproducts.

The purge stream comprising C₄ hydrocarbons taken from the light streammay be purged from the process in line 229 to avoid C₄ build up in theprocess. The purge stream comprising C₄ hydrocarbons in line 229 may besubjected to further processing to recover useful components or beblended in the gasoline pool.

The intermediate stream in intermediate line 222 may comprise at least70 wt % and suitably at least 90 wt % C₅ hydrocarbons which can then actas a solvent in the first oligomerization reactor zone 140 to maintainliquid phase therein. The overhead intermediate stream comprising C₅hydrocarbons should have less than 10 wt % C₄ or C₆ hydrocarbons andpreferably less than 1 wt % C₄ or C₆ hydrocarbons.

The intermediate stream may be condensed and recycled to the firstoligomerization reactor zone 140 as a first intermediate recycle streamin an intermediate recycle line 226 at a rate governed by control valve226′ to maintain the liquid phase in the oligomerization reactors 138,150 operating in the first oligomerization zone 130. The intermediatestream may comprise C₅ olefins that can oligomerize in theoligomerization zone. The C₅ hydrocarbon presence in the oligomerizationzone maintains the oligomerization reactors at liquid phase conditions.The pentanes are easily separated from the heavier olefinic product suchas in the depentanizer column 220. The pentane recycled to theoligomerization zone also dilutes the feed olefins to help limit thetemperature rise within the reactor due to the exothermicity of thereaction.

In an aspect, the intermediate stream in the intermediate line 222comprising C₅ hydrocarbons may be split into a purge stream in purgeline 228 and the first intermediate recycle stream comprising C₅hydrocarbons in the first intermediate recycle line 226. In an aspect,the first intermediate recycle stream in first intermediate recycle line226 taken from the intermediate stream in the intermediate line 222 isrecycled to the first oligomerization zone 130 downstream of theselective hydrogenation reactor 116. The intermediate stream inintermediate line 222 and the first intermediate recycle stream inintermediate recycle line 226 should be understood to be condensedoverhead streams. The recycle rate may be adjusted as necessary tomaintain liquid phase in the oligomerization reactors and to controltemperature rise, and/or to maximize selectivity to gasoline rangeoligomer products.

The purge stream comprising C₅ hydrocarbons taken from the intermediatestream may be purged from the process in line 228 to avoid C₅ paraffinbuild up in the process. The purge stream comprising C₅ hydrocarbons inline 228 may be subjected to further processing to recover usefulcomponents or be blended in the gasoline pool.

We have found that dimethyl sulfide boils with the C₅ hydrocarbons anddeactivates the unidimensional, 10-ring pore structured zeolite whichmay be the oligomerization catalyst. The mercaptan extraction unit 112may not remove sufficient dimethyl sulfide to avoid deactivating theoligomerization catalyst. Consequently, recycle of C₅ hydrocarbons tothe oligomerization zone 130 with oligomerization catalyst may beavoided by keeping valve 226′ shut unless sufficient dimethyl sulfidecan be successfully removed from the oligomerate stream or theoligomerization catalyst is not a unidimensional, 10-ring porestructured zeolite. However, the dimethyl sulfide does not substantiallyharm the solid phosphoric acid catalyst, so recycle of C₅ hydrocarbonsto the oligomerization zone 130 is suitable if SPA is theoligomerization catalyst.

Bypassing heavy oligomerate around the debutanizer column 210 and theoptional depentanizer column 220 enables the bottoms temperature to bediminished because relatively lighter material must be reboiled whichcan be achieved at a lower temperature and smaller heater duty in thedebutanizer column 210 and the optional depentanizer column 220.

At least a first portion of the heavy oligomerate flash stream in theheavy flash line 184 may be recycled to the oligomerization zone 130.The heavy oligomerate flash stream comprising C₆+ olefins in heavy flashline 184 may enter a process line 192 via a heavy inlet line 186. Atleast a first portion of the heavy flash oligomerate stream in a processline 192 may be taken as a recycle oligomerate stream in recycleoligomerate line 230 to the oligomerization zone 130. Consequently, theoligomerization zone 130 is in downstream communication with the heavyflash line 184 of the flash drum 180. Moreover, the process line 192 maybe in downstream communication with the heavy flash line 184. The heavyflash oligomerate stream in the process line 192 may have greater than10 wt % C₁₀ isoolefins. Flow through recycle oligomerate line 230 can beregulated by control valve 230′. Recycle of the heavy oligomerate fromthe flash drum 180 to the oligomerization zone 130 lowers utilityexpenses and lowers the required capacity of the debutanizer column 210and the depentanizer column 220 because the heavy oligomerate bypassesthe debutanizer column 210 and the depentanizer column 220. Flow of theheavy oligomerate flash stream from the heavy inlet line 186 to theprocess line 192 may be through an optional surge drum 190.

In an aspect, the process line 192 may be in downstream communicationwith the first product line 214 via route line 216 and a product inletline 234. The process line 192 may also be in downstream communicationwith the second product line 224 via the product inlet line 234. Atleast a first portion of the first liquid oligomerate product streamand/or the second liquid oligomerate product stream may be recycled inthe process line 192 and the recycle oligomerate line 230 to theoligomerization zone 130. Flow of at least a portion of the first liquidoligomerate product stream from the first product line 214 via routeline 216 and a product inlet line 234 and/or the second liquidoligomerate product stream from the second product line 224 via theproduct inlet line 234 to the process line 192 may be through anoptional surge drum 190.

In an aspect, the first liquid oligomerate product stream and/or thesecond liquid oligomerate product stream may be mixed with the heavyoligomerate flash stream to provide a mixed stream in the process line192. At least a first portion of this resulting mixed stream in theprocess line 192 may be recycled to the oligomerization feed line 132 ofthe oligomerization zone 130 through the recycle oligomerate line 230.Consequently, the oligomerization zone 130 is in downstreamcommunication with the heavy flash line 184 of the flash drum 180 and/orthe first liquid oligomerate product stream in the first product line214 from the debutanizer column 210 and/or the second liquid oligomerateproduct stream in the second product line 224 from the depentanizercolumn 220.

In an aspect, the first liquid oligomerate product stream and/or thesecond liquid oligomerate product stream may be mixed with the heavyoligomerate flash stream in the optional surge drum 190 and exit thesurge drum in the process line 192. Additionally, the oligomerizationzone 130 may be in downstream communication with the surge drum 190. Itis contemplated that a surge drum 190 need not be used to mix thesestreams, but that mixing may be achieved in the heavy inlet line 186,the product inlet line 234 and the process line 192.

The recycle oligomerate product stream comprising C₆+ olefins serves tomaintain liquid phase in the oligomerization zone 130 and providesolefins that can oligomerize to heavier diesel range olefins. In thisembodiment, the oligomerization zone 130 is in downstream communicationwith the first product line 214 of the debutanizer column 210 andperhaps the second product line 224 of the depentanizer column 220. In afurther aspect, the recycle oligomerate product line 230 is indownstream communication with the oligomerization zone 130.Consequently, the oligomerization zone 130 is in upstream and downstreamcommunication with the first product line 214, the second product line224 and the recycle oligomerate line 230.

A second portion of the heavy oligomerate flash stream from heavy flashline 184 may be processed as a heavy product stream in a heavy productline 196. In an aspect, a second portion of the first liquid oligomerateproduct stream from the first product line 214 and/or the second liquidoligomerate product stream from the second product line 224 may beprocessed as a heavy product stream in the heavy product line 196. In afurther aspect, when the heavy oligomerate flash stream and the liquidoligomerate product stream are mixed together to provide a mixed streamin process line 192, a second portion of the mixed stream may beprocessed as the heavy product stream in the heavy product line 196.

By recycling the recycle oligomerate product stream in the recycleoligomerate product line 230 from the first portion of the processstream in the process line 192 from which a second portion can be takenin heavy product line 196, an accumulation of heavy material in therecycle oligomerate product line 230 is avoided. Heavy material can betaken downstream in the heavy product line 196 to avoid accumulation inthe recycle oligomerate product stream. Recycle of the recycleoligomerate product stream directly from heavy flash line 184 would notprevent accumulation of heavy material in the recycle oligomerateproduct line 230. If a refiner desires to make additional propylene inthe FCC unit 20, a portion of the heavy product stream or the mixedstream in the heavy product line 196 comprising _(C6)+ olefins may berecycled to the FCC unit 20 in the FCC recycle line 280 as an FCCrecycle oligomerate stream. The FCC recycle oligomerate stream may betaken from the heavy product stream or the mixed stream in the heavyproduct line 196. A control valve 280′ on the FCC recycle line 280 maybe open if recycle of the heavy product stream or the mixed stream tothe FCC zone 20 is desired. In an aspect, the FCC recycle stream in theFCC recycle line 280 is in downstream communication with the FCCrecovery zone 200. In a further aspect, the FCC recycle line 280 is indownstream communication with the oligomerization zone 130. Hence, in anaspect, the FCC zone 20 is in upstream and downstream communication witholigomerization zone 130 and/or the FCC recovery zone 100. In a stillfurther aspect, FCC recycle line 280 is in upstream communication withthe FCC zone 20 to recycle heavy oligomerate for fluid catalyticcracking down to propylene or other light olefins. Lastly, the FCC zone20 may be in downstream communication with the heavy flash line 184and/or the first product line 214 and/or the second product line 224 andthe process line 192.

If the FCC zone 20 comprises a single reactor riser 26, the firstreactor riser 26 may be in downstream communication with the hydrocarbonfeed line 24 and the FCC recycle line 280. If the FCC zone 20 comprisesthe first reactor riser 26 and a second reactor riser 74, the firstreactor riser 26 may be in downstream communication with the hydrocarbonfeed line 24 and the second reactor riser 74 may be in downstreamcommunication with the FCC recycle line 280.

We have found that C₆+ oligomerate and distillate-range oligomeratesubjected to FCC is converted best over a blend of medium or smallerpore zeolite blended with a large pore zeolite such as Y zeolite asexplained previously with respect to the FCC zone 20. Additionally,oligomerate produced over the oligomerization catalyst in theoligomerization zone 130 provides an excellent feed to the FCC zone thatcan be cracked to yield greater quantities of propylene.

In an embodiment in which the oligomerization catalyst is SPA in theoligomerization zone 130 for oligomerizing C₄ olefins or a mixed C₄ andC₅ olefin stream, we have found that a gasoline product stream can beprovided in the heavy product line 196. The SPA catalyst minimizes theformation of C₁₂+ species with either a C₄ olefin or C₄ and C₅ olefinfeed. Consequently, even when heavier olefins than C₄ olefins arepresent in the oligomerization feed stream, the SPA catalyst manages tokeep C₁₂+ olefins present in the liquid oligomerate bottom productstream in the second product line 224 below less than about 20 wt % evenwhen over 85 wt % of feed olefins are converted and particularly whenover 90 wt % of C₄ olefins are converted to oligomerate.

Consequently, a gasoline oligomerate product stream may be collectedfrom the heavy product stream in a gasoline oligomerate product line 250and blended in the gasoline pool. The gasoline oligomerate product line250 may be in upstream communication with a gasoline tank 252 or agasoline blending line of a gasoline pool. However, further treatmentsuch as partial or full hydrogenation to reduce olefinicity may becontemplated. In such a case, a control valve 250′ may be all orpartially opened to allow C₆+ gasoline product to be sent to thegasoline tank 252 or the gasoline blending line.

In another aspect, a distillate separator feed stream may be taken in adistillate feed line 232 from the second portion of the heavyoligomerate flash stream from heavy flash line 184 in heavy product line196. In an additional aspect, a distillate separator feed stream may betaken in a distillate feed line 232 from the second portion of the firstliquid oligomerate product stream from the first product line 214 and/orthe second liquid oligomerate product stream from the second productline 224 in the heavy product line 196. In a further aspect, when theheavy oligomerate flash stream and the liquid oligomerate product streamare mixed together to provide a mixed stream in process line 192, adistillate separator feed stream may be taken in a distillate feed line232 from the second portion of the mixed stream in the heavy productline 196. Flow through the distillate feed line 232 can be regulated bycontrol valve 232′.

The oligomerization recovery zone 200 may also include a distillateseparator column 240 to which the heavy product stream comprisingoligomerate C₆+ hydrocarbons may be fed in distillate feed line 232taken from the heavy product line 196 for further separation. Thedistillate separator column 240 is in downstream communication with thefirst product line 214 of the debutanizer column 210, the second productline 224 of the depentanizer column 220, the heavy flash line 184 and/orthe process line 192.

The distillate separator column 240 separates the distillate separatoroligomerate feed stream into an gasoline overhead stream in an overheadline 242 comprising C₆, C₇, C₈, C₉, C₁₀ and/or C₁₁ olefins and a bottomdistillate stream comprising C₈+, C₉+, C₁₀+, C₁₁+, or C₁₂+ olefins in adiesel bottom line 244. When maximum production of distillate isdesired, the overhead pressure in the distillate separator column 240may be between about 10 and about 60 kPa (gauge) and the bottomtemperature may be between about 225° and about 275° C. When maximumproduction of gasoline is desired, the overhead pressure in thedistillate separator column 240 may be between about 10 and about 60 kPa(gauge) and the bottom temperature may be between about 190° and about250° C. The bottom temperature can be adjusted between about 175° andabout 275° C. to adjust the bottom product between a C₉+ olefin cut anda C₁₂+ olefin cut based on the heaviness of the diesel cut desired bythe refiner. The diesel bottoms stream in diesel bottoms line 244 mayhave greater than 30 wt % C₉+ isoolefins.

In an aspect, the gasoline overhead stream in gasoline overhead line 242may be recovered as product in product gasoline line 248 in downstreamcommunication with the recovery zone 200. The gasoline product streammay be subjected to further processing to recover useful components orblended in the gasoline pool. The gasoline product line 248 may be inupstream communication with a gasoline tank 252 or a gasoline blendingline of a gasoline pool. In this aspect, the overhead line 242 of thedistillate separator column 240 may be in upstream communication withthe gasoline tank 252 or the gasoline blending line.

In an aspect, the diesel product stream may be recovered as product in adiesel bottom line 244 in downstream communication with theoligomerization recovery zone 200. The diesel product stream may besubjected to further processing to recover useful components or blendedin the diesel pool. The diesel bottom line 244 may be in upstreamcommunication with a diesel tank 264 or a diesel blending line of adiesel pool. Additionally, LCO from LCO line 107 may also be blendedwith diesel in diesel bottom line 244.

Flow through the recycle oligomerate line 230, the FCC recycle line 280,the distillate feed line 232 and the gasoline oligomerate product line250 can be regulated by control valves 230′, 280′, 232′ and 250′,respectively, such that flow through each line can be shut off orallowed irrespective of the other lines.

In an aspect, a bypass line 194 may be in downstream communication withthe heavy flash line 184. Flow of the heavy flash stream through thebypass line is regulated by a control valve 194′. At least a portion ofthe heavy flash oligomerate stream may be bypassed around the processline 192 and the surge drum 190 to avoid recycling at least some of theheavy flash oligomerate to the oligomerization zone 130 and mixing theheavy flash oligomerate with the first liquid oligomerate product streamfrom first product line 214 and/or the second oligomerate product streamin the second product line 224 before the first portion of the firstliquid oligomerate product stream and the second oligomerate productstream is recycled to the oligomerization zone 130. The heavy flasholigomerate will have a larger molecular weight than the firstoligomerate product stream and/or the second oligomerate product stream.Hence, bypass of the heavy flash oligomerate stream in bypass line 194will decrease the molecular weight of the recycle oligomerate stream inrecycle oligomerate line 230 to the oligomerization zone 130.Consequently, the oligomerization to heavy oligomer in theoligomerization zone 130 is minimized because lighter oligomerate ispresent in the oligomerate recycle stream in recycle line 230. Thebypass line 194 may be out of upstream communication with theoligomerate recycle line 230 but may be in upstream communication withthe FCC recycle line 280, the distillate feed line 232 and the gasolineoligomerate product line 250. Accordingly, they bypass line 194 may feedthe bypassed portion of the heavy flash oligomerate as FCC recyclestream to the FCC zone 20 and/or as the distillate separator feed streamto the distillate separator column 240 and/or as to the gasoline tank252 or a gasoline blending line of a gasoline pool.

The invention will now be further illustrated by the followingnon-limiting examples.

EXAMPLES Example 1

Feed 1 in Table 2 was contacted with four catalysts to determine theireffectiveness in oligomerizing butenes.

TABLE 1 Component Fraction, wt % propylene 0.1 Iso-C₄'s 70.04isobutylene 7.7 1-butene 5.7 2-butene (cis and trans) 16.283-methyl-1-butene 0.16 acetone 0.02 Total 100

Catalyst A is an MTT catalyst purchased from Zeolyst having a productcode Z2K019E and extruded with alumina to be 25 wt % zeolite. Of MTTzeolite powder, 53.7 grams was combined with 2.0 grams Methocel and208.3 grams Catapal B boehmite. These powders were mixed in a mullerbefore a mixture of 18.2 g HNO₃ and 133 grams distilled water was addedto the powders. The composition was blended thoroughly in the muller toeffect an extrudable dough of about 52% LOI. The dough then was extrudedthrough a die plate to form cylindrical extrudates having a diameter ofabout 3.18 mm. The extrudates then were air dried, and calcined at atemperature of about 550° C. The MTT catalyst was not selectivated toneutralize surface acid sites such as with an amine.

Catalyst B is a SPA catalyst commercially available from UOP LLC.

Catalyst C is an MTW catalyst with a silica-to-alumina ratio of 36:1. OfMTW zeolite powder made in accordance with the teaching of U.S. Pat. No.7,525,008 B2, 26.4 grams was combined with and 135.1 grams Versal 251boehmite. These powders were mixed in a muller before a mixture of 15.2grams of nitric acid and 65 grams of distilled water were added to thepowders. The composition was blended thoroughly in the muller to effectan extrudable dough of about 48% LOI. The dough then was extrudedthrough a die plate to form cylindrical extrudates having a diameter ofabout 1/32″. The extrudates then were air dried and calcined at atemperature of about 550° C.

Catalyst D is an MFI catalyst purchased from Zeolyst having a productcode of CBV-8014 having a silica-to-alumina ratio of 80:1 and extrudedwith alumina at 25 wt % zeolite. Of MFI-80 zeolite powder, 53.8 gramswas combined with 205.5 grams Catapal B boehmite and 2 grams ofMethocel. These powders were mixed in a muller before a mixture of 12.1grams nitric acid and 115.7 grams distilled water were added to thepowders. The composition was blended thoroughly in the muller, then anadditional 40 grams of water was added to effect an extrudable dough ofabout 53% LOI. The dough then was extruded through a die plate to formcylindrical extrudates having a diameter of about 3.18 mm. Theextrudates then were air dried, and calcined at a temperature of about550° C.

The experiments were operated at 6.2 MPa and inlet temperatures atintervals between 160° and 240° C. to obtain different normal buteneconversions. Results are shown in FIGS. 2 and 3. In FIG. 2, C₈ toC₁₁olefin selectivity is plotted against normal butene conversion toprovide profiles for each catalyst.

Table 3 compares the RONC ±3 for each product by catalyst and provides akey to FIG. 3. The SPA catalyst B is superior, but the MTT catalyst A isthe least effective in producing gasoline range olefins.

TABLE 2 Catalyst RONC A MTT circles 92 B SPA diamonds 96 C MTW triangles97 D MFI-80 asterisks 95

The SPA catalyst was able to achieve over 95 wt % yield of gasolinehaving a RONC of >95 and with an Engler T90 value of 185° C. for theentire product. The T-90 gasoline specification is less than 193° C.

In FIG. 3, C₁₂+ olefin selectivity is plotted against normal buteneconversion to provide profiles for each catalyst. Table 4 compares thederived cetane number ±2 for each product by catalyst and provides a keyto FIG. 3.

TABLE 3 Catalyst Cetane A MTT circles 41 B SPA diamonds <14 C MTWtriangles 28 D MFI-80 asterisks 36

FIG. 3 shows that the MTT catalyst provides the highest C₁₂+ olefinselectivity which reaches over 70 wt %. These selectivities are from asingle pass of the feed stream through the oligomerization reactor.Additionally, the MTT catalyst provided C₁₂+ oligomerate with thehighest derived cetane. Cetane was derived using ASTM D6890 on the C₁₂+fraction at the 204° C. (400° F.) cut point. Conversely to gasolineselectivity, the MTT catalyst A is superior, but the SPA catalyst B isthe least effective in producing diesel range olefins.

The MTT catalyst was able to produce diesel with a cetane rating ofgreater than 40. The diesel cloud point was determined by ASTM D2500 tobe −66° C. and the T90 was 319° C. using ASTM D86 Method. The T90specification for diesel in the United States is between 282 and 338°C., so the diesel product meets the U.S. diesel standard.

Example 2

Two types of feed were oligomerized over oligomerization catalyst A ofExample 1, MTT zeolite. Feeds 1 and 2 contacted with catalyst A areshown in Table 4. Feed 1 is from Example 1.

TABLE 4 Feed 1 Feed 2 Component Fraction, wt % Fraction, wt % propylene0.1 0.1 isobutane 70.04 9.73 isobutylene 7.7 6.3 1-butene 5.7 4.92-methyl-2-butene 0 9.0 2-butene (cis & trans) 16.28 9.8 3-met-1-butene0.16 0.16 n-hexane 0 60 acetone 0.02 0.01 Total 100 100

In Feed 2, C₅ olefin is made up of 2-methyl-2-butene and3-methyl-1-butene which comprises 9.16 wt % of the reaction mixturerepresenting about a third of the olefins in the feed. 3-methyl-1-buteneis present in both feeds in small amounts. Propylene was present at lessthan 0.1 wt % in both feeds.

The reaction conditions were 6.2 MPa and a 1.5 WHSV. The maximumcatalyst bed temperature was 220° C. Oligomerization achievements areshown in Table 5.

TABLE 5 Feed 1 Feed 2 Inlet Temperature, ° C. 192 198 C₄ olefinconversion, % 98 99 nC₄ olefin conversion, % 97 99 C₅ olefin conversion,% n/a 95 C₅-C₇ selectivity, wt % 3 5 C₈-C₁₁ selectivity, wt % 26 40C₁₂-C₁₅ selectivity, wt % 48 40 C₁₆+ selectivity, wt % 23 16 Total C₉+selectivity, wt % 78 79 Total C₁₂+ selectivity, wt % 71 56 Net gasolineyield, wt % 35 44 Net distillate yield, wt % 76 77

Normal C₄ olefin conversion reached 99% with C₅ olefins in Feed 2 andwas 97 wt % without C₅ olefins in Feed 1. C₅ olefin conversion reached95%. With C₅ olefins in Feed 2, it was expected that a greaterproportion of heavier, distillate range olefins would be made. However,the Feed 2 with C₅ olefins oligomerized to a greater selectivity oflighter, gasoline range product in the C₅-C₇ and C₈-C₁₁ range and asmaller selectivity to heavier distillate range product in the C₁₂-C₁₅and C₁₆+ range.

This surprising result indicates that by adding C₅ olefins to the feed,a greater yield of gasoline can be made over Catalyst A, MTT. This isconfirmed by the greater net yield of gasoline and the lower selectivityto C₁₂+ fraction for Feed 2 than for Feed 1. Also, but not to the samedegree, by adding C₅ olefins to the feed, a greater yield of distillaterange material can be made. This is confirmed by the greater net yieldof distillate for Feed 2 than for Feed 1 on a single pass basis.Gasoline yield was classified by product meeting the Engler T90requirement and distillate yield was classified by product boiling over150° C. (300° F.).

Example 3

Three types of feed were oligomerized over oligomerization catalyst B ofExample 1, SPA. The feeds contacted with catalyst B are shown in Table6. Feed 2 is the same as Feed 2 in Example 2. Normal hexane andisooctane were used as heavy paraffin solvents with Feeds 2 and 3,respectively. All feeds had similar C₄ olefin levels and C₄ olefinspecies distributions. Feed 4 is similar to Feed 2 but has the pentenesevenly split between iso- and normal pentenes, which is roughly expectedto be found in an FCC product, and Feed 4 was diluted with isobutaneinstead of n-hexane.

TABLE 6 Feed 2 Feed 3 Feed 4 Component Fraction, wt % Fraction, wt %Fraction, wt % propylene 0.1 0.08 0.1 1,3-butadiene 0 0.28 0 isobutane9.73 6.45 69.72 isobutylene 6.3 7.30 6.3 1-butene 4.9 5.07 4.92-methyl-2-butene 9.0 0 4.5 2-butene (cis & trans) 9.8 11.33 9.83-met-1-butene 0.16 0.16 0.16 2-pentene 0 0 4.5 cyclopentane 0 0.28 0n-hexane 60 0 0 isooctane 0 60.01 0 acetone 0.01 0.01 0.02 Total 100 100100

The reaction pressure was 3.5 MPa. Oligomerization process conditionsand testing results are shown in Table 7.

TABLE 7 Feed 2 Feed 3 Feed 4 WHSV, hr⁻¹ .75 1.5 .75 Pressure, MPa 3.53.5 6.2 Inlet Temperature, ° C. 190 170 178 Maximum Temperature, ° C.198 192 198 Total C₄ olefin conversion, % 95 92 93 n-butene conversion,% 95 90 93 Total C₅ olefin conversion, % 90 n/a 86 C₅-C₇ selectivity, wt% 8 5 8 C₈-C₁₁ selectivity, wt % 77 79 77 C₁₂-C₁₅ selectivity, wt % 1516 15 C₁₆+ selectivity, wt % 0.3 0.1 .01 Total C₉+ selectivity, wt % 3520 25 Total C₁₂+ selectivity, wt % 17 16 15 Net gasoline yield, wt % 9492 91 Net distillate yield, wt % 32 18 23 RONC (±3) 97 96 96 EnglerT-90, ° C. 182 164 182

Net gasoline yield goes up to C₁₂− hydrocarbons and net distillate yieldgoes down to C₉+ hydrocarbons to account for different cut points thatmay be selected by a refiner. Olefin conversion was at least 90% andnormal butene conversion was over 90%. Normal butene conversion reached95% with C₅ olefins in Feed 2 and was 90% without C₅ olefins in Feed 3.C₅ olefin conversion reached 90% but was less when both iso- and normalC₅ olefins were in Feed 4.

It can be seen that the SPA catalyst minimized the formation of C₁₂+species to below 20 wt %, specifically, at 16 and 17 wt %, respectively,for feeds containing C₄ olefins or mixtures of C₄ and C₅ olefins in theoligomerization feed stream. When normal C₅ olefins were added, C₁₂+formation reduced to 15 wt %. The C₆+ oligomerate produced by all threefeeds met the gasoline T-90 spec indicating that 90 wt % boiled attemperatures under 193° C. (380° F.). The Research Octane Number for allthree products was high, over 95, with and without substantial C₅olefins present.

Example 4

Feed 2 with C₅ olefins present was subjected to oligomerization withCatalyst B, SPA, at different conditions to obtain different buteneconversions. C₅ olefin is made up of 2-methyl-2-butene and3-methyl-1-butene which comprises 9.16 wt % of the reaction mixturerepresenting about a third of the olefins in the feed. Propylene waspresent at less than 0.1 wt %. Table 8 shows the legend of componentolefins illustrated in FIG. 4.

TABLE 8 Component Symbols in FIG. 4 isobutylene Circle 1-butene Triangle2-methyl-2-butene and Diamond 3-met-1-butene 2-butene (cis & trans)Asterisk

FIG. 4 shows conversions for each of the olefins in Feed 2 over CatalystB, SPA. Over 95% conversion of normal C₄ olefins was achieved at over90% total butene conversion. Pentene conversion reached 90% at over 90%total butene conversion. Normal butene conversion actually exceededisobutene conversion at high butene conversion over about 95%.

Example 5

Three feeds were oligomerized to demonstrate the ability of Catalyst A,MTT, to produce diesel range oligomerate by recycling gasoline rangeoligomerate to the oligomerization zone. Feed 1 from Example 1 with anisobutane diluent was tested along with Feed 5 which had a normal hexanediluent and Feed 6 which had an isobutane diluent but spiked withdiisobutene to simulate the recycle of gasoline range oligomers to thereactor feed. The feeds are shown in Table 9. The symbols in FIG. 5correspond to those indicated in the last row of Table 9.

TABLE 9 Feed 1 Feed 5 Feed 6 Component Fraction, wt % Fraction, wt %Fraction, wt % propylene 0.1 0.08 0.08 isobutane 70.04 15.75 15.75isobutylene 7.7 7.3 7.3 1-butene 5.7 5.1 5.1 2-butene (cis & trans)16.28 11.6 11.6 3-met-1-butene 0.16 0.16 0.16 n-hexane 0 60 0 acetone0.02 0.01 0.01 tert-butyl alcohol 0 0.0008 0.0008 diisobutene 0 0 60Total 100 100 100 FIG. 5 symbol square diamond asterisk

The oligomerization conditions included 6.2 MPa pressure, 0.75 WHSV overCatalyst A, MTT. Normal butene conversion as a function of temperatureis graphed in FIG. 5 for the three feeds.

FIG. 5 demonstrates that Feed 6 with the diisobutene oligomer hasgreater normal butene conversion at equivalent temperatures between 180°and 240° C. Consequently, gasoline oligomerate recycle to theoligomerization zone will improve normal butene conversion. Buteneconversion for Feed 5 is shown in FIG. 6 and for Feed 6 is shown in FIG.7. The key for FIGS. 6 and 7 is shown in Table 10.

TABLE 10 Component Symbols in FIGS. 6 & 7 isobutylene Circle 1-buteneTriangle 2-butene (cis & trans) Asterisk

At higher butene conversions and with diisobutene recycle, isobutene hasthe lowest conversion with both 1-butene and 2-butene having greateroligomerization to oligomers. This result is probably due toback-cracking of diisobutene back to isobutene. However, withoutdiisobutene recycle, isobutene undergoes the greatest conversion, butwith 1-butene conversion apparently surpassing isobutene conversion atover 94% total butene conversion. This trend may be showing thatisobutene is more reactive and reaches a back-cracking limit faster,after which isobutene conversion is limited. We expect the sameperformance for Feed 1 with isobutane diluent.

Table 11 gives feed performance for the three feeds at conditionsselected to achieve high butene conversion and high C₁₂+ yield including6.2 MPa of pressure.

TABLE 11 Run Feed 1 Feed 5 Feed 6 WHSV, hr⁻¹ 0.9 0.6 0.7 Maximum BedTemperature, ° C. 240 236 239 Total C₄ olefin conversion, % 95 96 95n-butene conversion, % 95 95 97 isobutene conversion, % 96 97 911-butene conversion, % 97 98 97 2-butene conversion, % 94 94 97 C₅-C₇selectivity, wt % 3 3 0.8 C₈-C₁₁ selectivity, wt % 27 27 26 C₁₂-C₁₅selectivity, wt % 49 52 39 C₁₆+ selectivity, wt % 20 19 34 Total C₉+selectivity, wt % 76 77 77 Total C₁₂+ selectivity, wt % 70 71 73 DieselYield, wt % 72 74 73

C₁₂+ selectivity increased and C₁₆+ increased substantially with feedscontaining diisobutene compared with the feeds without diisobutene.Yield calculated by multiplying C₄ olefin conversion by total C₉+selectivity taken at the 150° C. (300° F.) cut point was over 70% forall feeds based on a single pass through the oligomerization reactor.

Example 6

Feed 1 and Feed 5 were reacted over Catalyst A, MTT, at 6.2 MPa and 0.75WHSV. A graph of selectivity as a function of maximum catalyst bedtemperature in FIG. 8 shows optimal maximum bed temperature betweenabout 220° and about 240° C. has an apex that corresponds with maximalC₁₂+ olefin selectivity and to a minimum C₈-C₁₁ olefin selectivity and aC₅-C₇ olefin selectivity. Table 12 provides a key for FIG. 8. In FIG. 8,solid points and lines represent Feed 1; whereas; hollow points anddashed lines represent Feed 5.

TABLE 12 Symbol Solid - Feed 1 Hollow - Feed 5 C₁₂+ olefin selectivityTriangles C₈-C₁₁ olefin selectivity Circles C₅-C₇ olefin selectivityGreek Crosses Asterisks

Example 7

Three different feeds representing product oligomerate were subjected tomicro reactor cracking testing over three different catalysts. The threefeeds were 2,4,4-trimethyl-1-pentene, 1-octene and mixed C₁₂ and largerolefins which contained linear molecules. The three catalysts included aZSM-5 additive with 40 wt % ZSM-5 crystals, Zeolite Y and a blend of 25wt % of the ZSM-5 additive and 75 wt % Zeolite Y such that 10 wt % ofthe blend was ZSM-5 crystals. The test conditions included 565° C., 10.3kPa (gauge) and a residence time of 0.05 seconds at standard feedconditions of 25° C. and atmospheric pressure. The feeds were a mixtureof 10 mol-% hydrocarbon, 5 mol-% steam, and the balance nitrogen. Table13 provides the key for FIGS. 9-11.

TABLE 13 Component Key Conversion, % Diagonal lines C₃ olefin yield, wt% Dotted fill C₄ olefin yield, wt % Cross Hatch C₅ olefin yield, wt %Diagonal Cross Hatch ZSM-5 Left Zeolite Y Middle Blend of ZSM-5 andZeolite Y Right Trimethyl pentene feed FIG. 9 1-Octene feed FIG. 10Mixed C₁₂ olefins FIG. 11

FIG. 9 reveals that achieving high conversion of2,4,4,-trimethyl-1-pentene over ZSM-5 alone was very difficult. The samefeed over Zeolite Y or the blend of ZSM-5 and Zeolite Y reached highconversion easily. The blend of ZSM-5 and Y zeolite had the highestpropylene yield. FIG. 10 shows that the conversion of 1-octene was veryhigh over all three catalysts. We saw a similar pattern for methylheptene in a separate test. Again, the blend of ZSM-5 and Y zeolite hadthe highest propylene yield. FIG. 11 shows that conversion of C₁₂ andlarger olefins, propylene tetramer, over the blend of ZSM-5 and Yzeolite had the highest propylene yield of all the feeds tested. ZSM-5alone was not able to achieve much conversion of the C₁₂ and largerolefin feed.

This example establishes that feeding oligomerate produced over CatalystA of Example 1, MTT, which produces less of the trimethyl pentene butmore of the linear and less-branched C₈ olefins and C₁₂ olefins to anFCC unit will provide the best FCC feed to crack into the mostpropylene.

Example 8

Three feeds were reacted over FCC equilibrium catalyst comprising 8 wt %ZSM-5. Feed 7 comprised hydrotreated VGO with a hydrogen content of 13.0wt %. Feed 8 comprised the same VGO mixed with 25 wt % oligomerateproduct catalyzed by Catalyst A of Example 1. Feed 9 comprised the sameVGO mixed with 25 wt % oligomerate product catalyzed by Catalyst B ofExample 1. The feeds were heated to 260-287° C. and contacted with theFCC catalyst in a riser apparatus to achieve 2.5-3.0 seconds ofresidence time. FIG. 12 plots C₃ olefin yield versus VGO conversion. Thekey for FIG. 13 is in Table 14.

TABLE 14 Feed Composition Key Feed 7 VGO Solid diamond Feed 8 VGO/MTToligomerate Square Feed 9 VGO/SPA oligomerate Triangle

FIG. 12 shows that recycle of oligomerate product to the FCC zone canboost propylene production. At the apex of the propylene yield curve ofVGO alone, the feed comprising VGO and oligomerate provided 3.2 wt %more propylene yield from the FCC zone.

Specific Embodiments

While the following is described in conjunction with specificembodiments, it will be understood that this description is intended toillustrate and not limit the scope of the preceding description and theappended claims.

A first embodiment of the invention is a process for making oligomerscomprising passing an oligomerization feed stream to an oligomerizationzone to oligomerize olefins in the oligomerization feed stream toproduce an oligomerate stream; separating the oligomerate stream fromthe oligomerization zone in a flash drum to provide a light flasholigomerate stream and a heavy flash oligomerate stream; fractionatingthe light flash oligomerate stream in a recovery zone; and recycling atleast a portion of the heavy flash oligomerate stream to theoligomerization zone. An embodiment of the invention is one, any or allof prior embodiments in this paragraph up through the first embodimentin this paragraph further comprising fractionating the light flasholigomerate stream to provide a product stream; mixing the productstream with the heavy flash oligomerate stream to provide a mixed streamand recycling at least a portion of the mixed stream to theoligomerization zone. An embodiment of the invention is one, any or allof prior embodiments in this paragraph up through the first embodimentin this paragraph further comprising feeding a portion of the mixedstream to an FCC zone. An embodiment of the invention is one, any or allof prior embodiments in this paragraph up through the first embodimentin this paragraph further comprising taking a distillate separator feedstream from the mixed stream and separating the distillate separatorfeed stream into a gasoline stream and a distillate stream. Anembodiment of the invention is one, any or all of prior embodiments inthis paragraph up through the first embodiment in this paragraph whereinthe fractionation comprises fractionating the light flash oligomeratestream to provide a light stream comprising C₄ hydrocarbons and a firstoligomerate stream comprising C₅ hydrocarbons. An embodiment of theinvention is one, any or all of prior embodiments in this paragraph upthrough the first embodiment in this paragraph further comprisingfractionating the first oligomerate stream to provide an intermediatestream and a product stream; mixing the product stream with the heavyflash oligomerate stream to provide a mixed stream and recycling atleast a portion of the mixed stream to the oligomerization zone. Anembodiment of the invention is one, any or all of prior embodiments inthis paragraph up through the first embodiment in this paragraph furthercomprising feeding a portion of the mixed stream to an FCC zone ortaking a distillate separator feed stream from the mixed stream andseparating the distillate separator feed stream into a gasoline streamand a distillate stream. An embodiment of the invention is one, any orall of prior embodiments in this paragraph up through the firstembodiment in this paragraph further comprising debutanizing the lightflash oligomerate stream to additionally provide a product stream;mixing the product stream with the heavy flash oligomerate stream toprovide a mixed stream and recycling at least a portion of the mixedstream to the oligomerization zone. An embodiment of the invention isone, any or all of prior embodiments in this paragraph up through thefirst embodiment in this paragraph further comprising feeding a portionof the mixed stream to an FCC zone or taking a distillate separator feedstream from the mixed stream and separating the distillate separatorfeed stream into a gasoline stream and a distillate stream. Anembodiment of the invention is one, any or all of prior embodiments inthis paragraph up through the first embodiment in this paragraph furthercomprising bypassing a portion of the heavy flash oligomerate stream toavoid recycling to the oligomerization zone and feeding the portion tothe FCC zone or feeding the portion as a distillate separator feedstream and separating the distillate separator feed stream into agasoline stream and a distillate stream.

A second embodiment of the invention is a process for making oligomerscomprising passing an oligomerization feed stream to an oligomerizationzone to oligomerize C₄ olefins in the oligomerization feed stream toproduce an oligomerate stream; separating the oligomerate stream fromthe oligomerization zone in a flash drum to provide a light flasholigomerate stream and a heavy flash oligomerate stream; fractionatingthe light flash oligomerate stream in a recovery zone; recycling atleast a portion of the heavy flash oligomerate stream to theoligomerization zone; and bypassing a bypass portion of the heavy flasholigomerate stream to avoid recycling to the oligomerization zone. Anembodiment of the invention is one, any or all of prior embodiments inthis paragraph up through the second embodiment in this paragraphfurther comprising feeding the bypass portion to the FCC zone or feedingthe portion as a distillate separator feed stream and separating thedistillate separator feed stream into a gasoline stream and a distillatestream. An embodiment of the invention is one, any or all of priorembodiments in this paragraph up through the second embodiment in thisparagraph further comprising fractionating the light flash oligomeratestream to provide a product stream and recycling a portion of theproduct stream to the oligomerization zone. An embodiment of theinvention is one, any or all of prior embodiments in this paragraph upthrough the second embodiment in this paragraph wherein thefractionation comprises debutanizing the light flash oligomerate streamto provide a light stream comprising C₄ hydrocarbons and a firstoligomerate stream comprising C₅ hydrocarbons. An embodiment of theinvention is one, any or all of prior embodiments in this paragraph upthrough the second embodiment in this paragraph further comprisingdepentanizing the first oligomerate stream to provide an intermediatestream and a product stream and recycling at least a portion of theproduct stream to the oligomerization zone. An embodiment of theinvention is one, any or all of prior embodiments in this paragraph upthrough the second embodiment in this paragraph further comprisingfeeding a portion of the bypass portion to an FCC zone or taking adistillate separator feed stream from the mixed stream and separatingthe distillate separator feed stream into a gasoline stream and adistillate stream.

A third embodiment of the invention is a process for making oligomerscomprising passing an oligomerization feed stream to an oligomerizationzone to oligomerize olefins in the oligomerization feed stream toproduce an oligomerate stream; separating the oligomerate stream fromthe oligomerization zone in a flash drum to provide a light flasholigomerate stream and a heavy flash oligomerate stream; fractionatingthe light flash oligomerate stream in a recovery zone to provide aproduct stream; mixing the product stream with the heavy flasholigomerate stream to provide a mixed stream; and recycling at least aportion of the mixed stream to the oligomerization zone. An embodimentof the invention is one, any or all of prior embodiments in thisparagraph up through the third embodiment in this paragraph furthercomprising feeding a portion of the mixed stream to an FCC zone ortaking a distillate separator feed stream from the mixed stream andseparating the distillate separator feed stream into a gasoline streamand a distillate stream. An embodiment of the invention is one, any orall of prior embodiments in this paragraph up through the thirdembodiment in this paragraph wherein the fractionation comprisesdebutanizing the light flash oligomerate stream to provide a lightstream comprising C₄ hydrocarbons and a first oligomerate streamcomprising C₅ hydrocarbons. An embodiment of the invention is one, anyor all of prior embodiments in this paragraph up through the thirdembodiment in this paragraph further comprising depentanizing the firstoligomerate stream to provide an intermediate stream and the productstream or further debutanizing the light flash oligomerate stream toadditionally provide the product stream.

A fourth embodiment of the invention is an apparatus for makingoligomers comprising an oligomerization zone for oligomerizing olefinsin the oligomerization feed stream to produce an oligomerate stream; aflash drum for separating the oligomerate stream in communication withthe oligomerization zone; a light flash line from the flash drum and aheavy flash line from the flash drum with an inlet to the light flashline above an inlet to the heavy flash line; a fractionation column incommunication with the light flash line for fractionating the lightflash oligomerate stream; and the oligomerization zone in downstreamcommunication with the heavy flash line. An embodiment of the inventionis one, any or all of prior embodiments in this paragraph up through thefourth embodiment in this paragraph further comprising a product line indownstream communication with the fractionation column and a recycleline in downstream communication with the heavy flash line and theproduct line. An embodiment of the invention is one, any or all of priorembodiments in this paragraph up through the fourth embodiment in thisparagraph further comprising a process line in downstream communicationwith the product line and the heavy flash line and the oligomerizationzone is in downstream communication with the process line via therecycle line. An embodiment of the invention is one, any or all of priorembodiments in this paragraph up through the fourth embodiment in thisparagraph further comprising an FCC zone in downstream communicationwith the heavy flash line and the product line. An embodiment of theinvention is one, any or all of prior embodiments in this paragraph upthrough the fourth embodiment in this paragraph further comprising adistillate separator in downstream communication with the heavy flashline and the product line. An embodiment of the invention is one, any orall of prior embodiments in this paragraph up through the fourthembodiment in this paragraph wherein the fractionation column is adebutanizer column. An embodiment of the invention is one, any or all ofprior embodiments in this paragraph up through the fourth embodiment inthis paragraph further comprising the debutanizer column in a recoveryzone and a depentanizer column in the recovery zone; the depentanizercolumn in downstream communication with a bottoms line from thedebutanizer; and the product line comes from the bottom of thedepentanizer column. An embodiment of the invention is one, any or allof prior embodiments in this paragraph up through the fourth embodimentin this paragraph further comprising the product line comes from thebottom of the debutanizer column. An embodiment of the invention is one,any or all of prior embodiments in this paragraph up through the fourthembodiment in this paragraph further comprising a bypass line indownstream communication with the heavy flash line and a process line indownstream communication with the heavy flash line; the bypass linebeing out of communication with the recycle line.

A fifth embodiment of the invention is an apparatus for making oligomerscomprising an oligomerization zone for oligomerizing olefins in theoligomerization feed stream to produce an oligomerate stream; a flashdrum for separating the oligomerate stream in communication with theoligomerization zone; a light flash line from the flash drum and a heavyflash line from the flash drum with an inlet to the light flash lineabove an inlet to the heavy flash line; a fractionation column incommunication with the light flash line for fractionating the lightflash oligomerate stream; a product line in downstream communicationwith the fractionation column; a recycle line in downstreamcommunication with the heavy flash line and the product line; theoligomerization zone in downstream communication with the recycle line.An embodiment of the invention is one, any or all of prior embodimentsin this paragraph up through the fifth embodiment in this paragraphfurther comprising a surge drum in downstream communication with theproduct line and the heavy flash line and the oligomerization zone is indownstream communication with the surge drum via the recycle line. Anembodiment of the invention is one, any or all of prior embodiments inthis paragraph up through the fifth embodiment in this paragraph furthercomprising a process line in downstream communication with the productline and the heavy flash line and the recycle line is in downstreamcommunication with the process line. An embodiment of the invention isone, any or all of prior embodiments in this paragraph up through thefifth embodiment in this paragraph further comprising an FCC zone indownstream communication with the process line. An embodiment of theinvention is one, any or all of prior embodiments in this paragraph upthrough the fifth embodiment in this paragraph further comprising adistillate separator in downstream communication with the process line.An embodiment of the invention is one, any or all of prior embodimentsin this paragraph up through the fifth embodiment in this paragraphwherein the fractionation column is a debutanizer column. An embodimentof the invention is one, any or all of prior embodiments in thisparagraph up through the fifth embodiment in this paragraph furthercomprising the debutanizer column in a recovery zone and a depentanizercolumn in the recovery zone; the depentanizer column in downstreamcommunication with a bottoms line from the debutanizer; and the productline comes from the bottom of the depentanizer column. An embodiment ofthe invention is one, any or all of prior embodiments in this paragraphup through the fifth embodiment in this paragraph further comprising theproduct line comes from the bottom of the debutanizer column. Anembodiment of the invention is one, any or all of prior embodiments inthis paragraph up through the fifth embodiment in this paragraph furthercomprising a bypass line in downstream communication with the heavyflash line and a process line in downstream communication with the heavyflash line; the bypass line being out of communication with the recycleline.

A sixth embodiment of the invention is an apparatus for making oligomerscomprising an oligomerization zone for oligomerizing olefins in theoligomerization feed stream to produce an oligomerate stream; a flashdrum for separating the oligomerate stream in communication with theoligomerization zone; a light flash line from the flash drum and a heavyflash line from the flash drum with an inlet to the light flash lineabove an inlet to the heavy flash line; a recovery zone in communicationwith the light flash line for fractionating the light flash oligomeratestream; and the oligomerization zone in downstream communication withthe heavy flash line. An embodiment of the invention is one, any or allof prior embodiments in this paragraph up through the sixth embodimentin this paragraph further comprising a process line in downstreamcommunication with the product line and the heavy flash line and arecycle line is in downstream communication with the process line; theoligomerization zone being in downstream communication with the recycleline and an FCC zone or an distillate separator is in downstreamcommunication with the process line.

Without further elaboration, it is believed that one skilled in the artcan, using the preceding description, utilize the present invention toits fullest extent. Preferred embodiments of this invention aredescribed herein, including the best mode known to the inventors forcarrying out the invention. The preceding preferred specific embodimentsare, therefore, to be construed as merely illustrative, and notlimitative of the remainder of the disclosure in any way whatsoever.

In the foregoing, all temperatures are set forth in degrees Celsius and,all parts and percentages are by weight, unless otherwise indicated.Pressures are given at the vessel outlet and particularly at the vaporoutlet in vessels with multiple outlets. Control valves should be openedor closed as consistent with the intent of the disclosure.

From the foregoing description, one skilled in the art can easilyascertain the essential characteristics of this invention and, withoutdeparting from the spirit and scope thereof, can make various changesand modifications of the invention to adapt it to various usages andconditions.

1. An apparatus for making oligomers comprising: an oligomerization zonefor oligomerizing olefins in an oligomerization feed stream to producean oligomerate stream including hydrocarbons; a flash drum forseparating said oligomerate stream in communication with saidoligomerization zone; a light flash line from the flash drum and a heavyflash line from the flash drum with an inlet to the light flash lineabove an inlet to the heavy flash line, wherein the heavy flash line isconfigured and arranged to receive the heaviest hydrocarbons from saidoligomerate stream; a fractionation column in communication with saidlight flash line for fractionating said light flash oligomerate stream;and said oligomerization zone in downstream communication with saidheavy flash line, and wherein said heavy flash line bypasses saidfractionation column.
 2. The apparatus of claim 1 further comprising aproduct line in downstream communication with said fractionation columnand a recycle line in downstream communication with said heavy flashline and said product line.
 3. The apparatus of claim 2 furthercomprising a process line in downstream communication with said productline and said heavy flash line and said oligomerization zone is indownstream communication with said process line via said recycle line.4. The apparatus of claim 2 further comprising an FCC zone in downstreamcommunication with said heavy flash line and said product line.
 5. Theapparatus of claim 2 further comprising a distillate separator indownstream communication with said heavy flash line and said productline.
 6. The apparatus of claim 2 wherein said fractionation column is adebutanizer column.
 7. The apparatus of claim 6 further comprising saiddebutanizer column in a recovery zone and a depentanizer column in saidrecovery zone; said depentanizer column in downstream communication witha bottoms line from said debutanizer; and said product line comes fromthe bottom of the depentanizer column.
 8. The apparatus of claim 6further comprising said product line comes from the bottom of thedebutanizer column.
 9. The apparatus of claim 2 further comprising abypass line in downstream communication with said heavy flash line and aprocess line in downstream communication with said heavy flash line;said bypass line being out of communication with said recycle line. 10.An apparatus for making oligomers comprising: an oligomerization zonefor oligomerizing olefins in an oligomerization feed stream to producean oligomerate stream including hydrocarbons; a flash drum forseparating said oligomerate stream in communication with saidoligomerization zone; a light flash line from the flash drum and a heavyflash line from the flash drum with an inlet to the light flash lineabove an inlet to the heavy flash line, wherein the heavy flash line isconfigured and arranged to receive the heaviest hydrocarbons from saidoligomerate stream; a fractionation column in communication with saidlight flash line for fractionating said light flash oligomerate stream;a product line in downstream communication with said fractionationcolumn; a recycle line in downstream communication with said heavy flashline and said product line; said oligomerization zone in downstreamcommunication with said recycle line, and a process line in downstreamcommunication with said product line and said heavy flash line, whereinand said recycle line is in downstream communication with said processline.
 11. The apparatus of claim 10 further comprising a surge drum indownstream communication with said product line and said heavy flashline and said oligomerization zone is in downstream communication withsaid surge drum via said recycle line.
 12. (canceled)
 13. The apparatusof claim 12 further comprising an FCC zone in downstream communicationwith said process line.
 14. The apparatus of claim 12 further comprisinga distillate separator in downstream communication with said processline.
 15. The apparatus of claim 10 wherein said fractionation column isa debutanizer column.
 16. The apparatus of claim 15 further comprisingsaid debutanizer column in a recovery zone and a depentanizer column insaid recovery zone; said depentanizer column in downstream communicationwith a bottoms line from said debutanizer; and said product line comesfrom the bottom of the depentanizer column.
 17. The apparatus of claim15 further comprising said product line comes from the bottom of thedebutanizer column.
 18. The apparatus of claim 15 further comprising abypass line in downstream communication with said heavy flash line and aprocess line in downstream communication with said heavy flash line;said bypass line being out of communication with said recycle line. 19.An apparatus for making oligomers comprising: an oligomerization zonefor oligomerizing olefins in an oligomerization feed stream to producean oligomerate stream including hydrocarbons; a flash drum forseparating said oligomerate stream in communication with saidoligomerization zone; a light flash line from the flash drum and a heavyflash line from the flash drum with an inlet to the light flash lineabove an inlet to the heavy flash line, wherein the heavy flash line isconfigured and arranged to receive the heaviest hydrocarbons from saidoligomerate stream; a recovery zone in communication with said lightflash line for fractionating said light flash oligomerate stream; saidoligomerization zone in downstream communication with said heavy flashline; and a process line in downstream communication with said heavyflash line and a recycle line in downstream communication with saidprocess line; said oligomerization zone being in downstreamcommunication with said recycle line and an FCC zone or a distillateseparator being in downstream communication with said process line. 20.(canceled)